🎨 Colour Does Not Exist

The Brain's Greatest Illusion
How the Universe Contains Only Light, While Our Minds Paint Reality

By Dhinakar Rajaram

Foreword

Every now and then, science presents us with an idea so profound that it quietly reshapes the way we see the world. This article explores one such idea—one that at first sounds impossible, even absurd:

"Colour does not exist."

Of course, sunsets glow in brilliant shades of orange and crimson, forests shimmer in countless greens, oceans reflect deep blues, and flowers burst with vivid colours. We experience them every moment of our lives. Yet, from the perspective of modern physics, none of these colours actually exist as physical properties of the external universe.

Outside our eyes and brains, there are no reds, blues, greens or yellows. There are only photons—tiny packets of electromagnetic energy—travelling through space with different wavelengths. Colour appears only after those photons interact with specialised cells inside our eyes and are interpreted by one of the most sophisticated information-processing systems known: the human brain.

This blog takes you on a journey across multiple branches of science—physics, astronomy, neuroscience, biology, psychology, evolution and photography—to understand how our perception of colour is constructed, why the night sky appears grey to our eyes, why astronomical photographs reveal colours invisible to us, why black-and-white photography often evokes stronger emotions, and what this remarkable illusion tells us about reality itself.

Rather than simply presenting scientific facts, this article aims to encourage readers to pause, question familiar assumptions, and appreciate the extraordinary mechanisms through which our brains transform streams of invisible electromagnetic radiation into the colourful world we experience every waking moment.

Perhaps, by the end of this journey, you will never look at the sky—or at colour itself—in quite the same way again.

About This Article

This is a long-form science article intended for curious readers, students, educators, amateur astronomers, photographers, and anyone fascinated by how the human mind interprets reality. Depending upon your reading speed, completing this article may take approximately 30–45 minutes.

Every effort has been made to explain complex scientific concepts using clear language, everyday examples, original illustrations, and carefully selected analogies without sacrificing scientific accuracy.

Throughout the article, physics, astronomy, neuroscience, evolutionary biology and visual perception are woven together to reveal one of nature's most fascinating truths—that what we experience as colour is not a property of the external universe, but a remarkable creation of the brain.

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While every translation attempts to preserve the original meaning, some scientific terminology and nuances may be expressed differently across languages. For the most accurate interpretation of the concepts discussed, the English version remains the reference edition.

Preface

Imagine standing beneath a clear night sky far from city lights. Above you stretches the magnificent Milky Way—a vast river of countless stars extending across the heavens. It appears soft, pale and almost monochrome. Yet when astronomers photograph that very same sky using sensitive cameras and long exposures, it explodes into breathtaking shades of crimson hydrogen clouds, turquoise oxygen nebulae, golden star fields and delicate blue reflection nebulae.

Which view is correct?

Surprisingly, both are.

The colourful photograph is not revealing colours that physically exist in space waiting to be discovered. Rather, it records photons that our eyes simply cannot collect efficiently enough. Meanwhile, our own visual system quietly constructs an entirely different representation of reality—one optimised not for scientific accuracy, but for survival.

The deeper scientists have explored the nature of light, vision and the brain over the past three centuries, the more astonishing the story has become. What began with Isaac Newton's experiments using prisms eventually evolved into discoveries in quantum physics, neurobiology and cognitive science, revealing that colour is neither stored inside objects nor travelling through space.

Instead, colour is an experience.

It is an electrochemical sensation generated by billions of neurons interpreting patterns of electromagnetic radiation. It exists nowhere outside conscious observers.

This simple statement carries enormous philosophical implications. It reminds us that the world we experience is not reality itself, but a remarkably sophisticated interpretation of reality—one assembled continuously by our nervous system from incomplete sensory information.

In the pages that follow, we shall journey from the Sun to distant galaxies, from the retina to the visual cortex, from Newton's prism to the Hubble Space Telescope, from black-and-white photography to the colourful dreams painted inside the human mind.

Welcome to one of the greatest illusions ever created by nature.

The Universe Without Colour
What Exactly Is Light?
The Electromagnetic Spectrum
How Objects Reflect Wavelengths
The Human Eye: Rods and Cones
How the Brain Manufactures Colour
Why Purple Doesn't Exist in the Spectrum
Why Space Appears Grey
Astronomical Photography and Long Exposures
False Colour Images in Astronomy
Evolution's Colour Palette
Animals That See Different Worlds
Colour Blindness and Human Diversity
Optical Illusions and Brain Predictions
Why Black-and-White Photography Feels Different
Does Reality Have Any Colour At All?
Final Reflections: Living Inside a Painted Dream
Glossary
References & Further Reading

PART I
The Universe Without Colour

"Before we understand colour, we must first understand light. Before we understand light, we must first question what we believe we see."

Section 1 – What Does It Mean to Say “Colour Does Not Exist”?

Imagine waking up tomorrow morning to discover that every colour you have ever seen—the blue sky, the green forests, the crimson sunset, the golden glow of autumn leaves and the brilliant rainbow after a passing shower—never actually existed in the world around you.

At first glance, the statement seems absurd. After all, colour appears to be one of the most obvious characteristics of the Universe. Every object seems to possess its own colour. A ripe tomato is red, a banana is yellow, emeralds are green, sapphires are blue and snow is white. We have built languages, cultures, art and even emotions around colours.

Yet modern science tells a very different story.

The Universe itself contains no redness, blueness or greenness. It contains no yellows, purples, oranges or pinks either. Beyond our eyes and brains, there are only atoms, molecules, electromagnetic radiation and the laws of physics governing their interactions.

This does not mean that colours are imaginary or that what we see is somehow false. Rather, it means that colour is not an intrinsic property existing independently in nature. Instead, colour is a perceptual experience—an extraordinary sensation constructed by our nervous system after it receives information carried by light.

In other words, the Universe provides the data. The brain creates the experience.

This distinction is subtle but profound. It challenges one of the deepest assumptions we make every day—that the colourful world we perceive is identical to the physical world that exists outside us.

The more scientists have studied light, vision and the brain over the past three centuries, the more remarkable the picture has become. The photons arriving from the Sun carry energy, momentum and wavelength, but they carry no labels saying "red", "green" or "blue". Those labels are invented by the brain after the light has already reached our eyes.

Consider another familiar example.

If you stand beneath a clear night sky, the magnificent Milky Way appears as a faint grey band stretching across the heavens. Through the eyepiece of a telescope, most nebulae and galaxies also appear grey or slightly greenish. Yet the spectacular photographs published by observatories reveal vivid crimson hydrogen clouds, brilliant blue reflection nebulae and glowing golden star fields.

Which view is the real one?

The answer is both—and neither.

The camera records photons over many minutes or even hours, collecting far more light than the human eye can gather in a fraction of a second. Our eyes, constrained by biology, often cannot activate the colour-sensitive cone cells under such dim conditions. Consequently, the brain receives little or no colour information to process, and the Universe appears almost monochrome.

This simple astronomical observation hints at a profound truth: colour is not something that exists "out there" waiting to be discovered. It emerges only when sufficient light interacts with the visual system of an observer.

But perhaps the easiest way to understand this idea is through a simple thought experiment.

A Thought Experiment

Imagine placing a perfectly ripe red apple inside a completely dark, sealed room.

The apple continues to exist. Its atoms remain exactly where they were. Its chemical composition does not change. Its mass, shape and texture remain unaltered.

But is the apple still red?

Without light illuminating its surface, no photons are reflected towards an observer. Without reflected photons, the retina receives no visual information. Without signals travelling along the optic nerve, the brain has nothing from which to construct the sensation of redness.

The object certainly exists.

Its colour, however, does not.

Only when light illuminates the apple, enters the eye and is processed by the brain does the familiar sensation we call red come into existence.

Colour therefore is not solely a property of an object, nor solely a property of light. It is the result of an interaction between three essential participants:

The source of light.
The object interacting with that light.
An observer possessing a visual system capable of interpreting the reflected radiation.

Remove any one of these three, and colour disappears.

This simple observation leads us to one of the most beautiful conclusions in modern science.

The Universe contains light.
Objects interact with light.
The eye detects light.
The brain creates colour.

Everything that follows in this article builds upon this single idea. To understand why colour does not exist as an independent physical entity, we must first understand what actually travels through space from the Sun to our eyes.

That journey begins not with colour, but with one of nature's most fundamental phenomena: light itself.

SUN │ ▼ Electromagnetic Radiation │ ▼ An Object (absorbs & reflects light) │ ▼ Human Eye │ ▼ Electrical Signals │ ▼ Brain │ ▼ Perception of Colour

Section 2 – The Universe Speaks the Language of Light

If colour is not travelling from the Sun to our eyes, then what exactly is?

The answer is one of the most fundamental entities in physics: light.

Everything we see, from a candle flame flickering in a dark room to the most distant galaxy ever photographed by the James Webb Space Telescope, reaches us through light. It is the messenger of the Universe, carrying information across enormous distances at the astonishing speed of approximately 2,99,792 kilometres per second (1,86,282 miles per second) in a vacuum.

Yet light itself has no colour.

This statement may seem surprising because we often speak of "red light", "blue light" or "green light". Scientifically, however, these are simply convenient descriptions of different wavelengths within a small portion of the electromagnetic spectrum. The photons themselves are not coloured. They are packets of electromagnetic energy characterised by properties such as wavelength, frequency and energy—not by the sensations that arise later within the human brain.

To understand this, imagine receiving a letter written in an unfamiliar language.

The paper contains symbols and information, but the meaning does not exist within the ink itself. Meaning arises only when a reader interprets those symbols.

Light behaves in much the same way.

Photons carry physical information about the Universe. They tell us about the temperature of stars, the composition of distant galaxies, the atmosphere of planets and the surfaces of everyday objects. However, the sensation of colour emerges only when the brain decodes this information after the photons have entered our eyes.

In this sense, light is the language spoken by the Universe, while colour is the language spoken by the brain.

Light: Both a Wave and a Particle

One of the greatest discoveries of twentieth-century physics was that light exhibits a remarkable dual nature. Depending upon how we observe it, light behaves both as a continuous electromagnetic wave and as tiny discrete packets of energy called photons.

This phenomenon, known as wave-particle duality, lies at the heart of quantum physics.

When light spreads through space, it behaves like a wave. It can interfere with itself, bend around obstacles and produce beautiful diffraction patterns. Yet when it interacts with matter—for example, when it strikes the retina of your eye—it behaves as though it consists of individual photons, each carrying a precise amount of energy.

Every second, trillions upon trillions of photons enter your eyes. Each one carries information gathered during its journey through space. Some have travelled only a few metres after reflecting from a nearby object, while others began their journey millions or even billions of years ago from distant stars and galaxies.

Remarkably, despite carrying all this information, none of these photons possesses colour.

Wavelength: The Invisible Signature of Light

If photons are not coloured, why do we perceive different colours?

The answer lies in a physical property called wavelength.

Imagine gentle waves travelling across the surface of a calm lake. Some waves have long distances between successive crests, while others are packed much more closely together.

Light behaves in a similar manner.

Electromagnetic waves differ in the distance between one crest and the next. This distance is called the wavelength, and it is usually measured in nanometres (nm), where one nanometre is one-billionth of a metre.

Visible light occupies only a tiny range of wavelengths, approximately between 380 nanometres and 750 nanometres. Waves near the shorter end of this range stimulate our visual system in ways that we perceive as violet or blue, while longer wavelengths eventually give rise to sensations such as orange and red.

Notice something important.

The wavelength itself is a measurable physical quantity. Scientists can determine it using instruments, even in the complete absence of a human observer.

Colour, however, is different.

Colour appears only after those wavelengths are detected by specialised cells inside the retina and interpreted by neural circuits within the brain.

In other words, wavelength belongs to physics. Colour belongs to perception.

Figure 2. Light leaves the Sun as electromagnetic radiation. After interacting with objects, some of this light enters the eye, where it is converted into electrical signals. Only when these signals are processed by the brain does the sensation of colour emerge.

A Universe Filled with Invisible Light

Perhaps the most astonishing fact of all is that the light visible to our eyes represents only a tiny fraction of the electromagnetic radiation filling the Universe.

Radio waves carrying television broadcasts, microwaves heating food, infrared radiation emitted by warm objects, ultraviolet rays from the Sun, X-rays used in medicine and highly energetic gamma rays produced by exploding stars are all forms of exactly the same phenomenon.

They differ only in wavelength and energy.

The colourful world we experience is therefore based on a remarkably narrow window of the electromagnetic spectrum—a tiny slice of reality to which evolution has tuned the human eye.

To appreciate just how small that window is, we must now explore the complete electromagnetic spectrum.

Section 3 – The Electromagnetic Spectrum: Our Tiny Window on Reality

The human eye often gives us the comforting illusion that we are seeing the world as it truly is. We look around and assume that the colourful landscape before us represents the whole of reality.

Nothing could be further from the truth.

The visible colours we experience occupy only an extraordinarily small portion of the electromagnetic spectrum—the complete family of electromagnetic radiation that fills the Universe. Beyond the narrow range that our eyes can detect lies an immense invisible world stretching across wavelengths both vastly longer and unimaginably shorter than visible light.

Imagine standing on the shore of a vast ocean and collecting a single teaspoon of water. The tiny amount of water in the spoon represents visible light, while the entire ocean represents the electromagnetic spectrum. This comparison is not exact, but it conveys the same astonishing idea: the fraction of reality accessible to human vision is remarkably small.

Every form of electromagnetic radiation—whether it is a radio signal received by your mobile phone, the microwaves heating your lunch, the infrared radiation emitted by a warm cup of tea, the ultraviolet rays from the Sun, the X-rays used to examine broken bones or the gamma rays produced by exploding stars—is fundamentally the same phenomenon.

The only differences are their wavelength, frequency and energy.

The Electromagnetic Family

Scientists classify electromagnetic radiation into several regions based upon wavelength and frequency. Although we give them different names, they are all manifestations of the same physical phenomenon.

Region	Approximate Wavelength	Common Applications
Radio Waves	More than 1 metre	Broadcasting, communication, radio astronomy
Microwaves	1 metre to 1 millimetre	Microwave ovens, radar, Wi-Fi, satellites
Infrared	1 mm to 700 nm	Heat radiation, thermal imaging, astronomy
Visible Light	Approximately 380–750 nm	Human vision
Ultraviolet	380–10 nm	Sterilisation, astronomy, fluorescence
X-rays	10–0.01 nm	Medical imaging, crystallography
Gamma Rays	Less than 0.01 nm	Nuclear processes, supernovae, cosmic events

Our Tiny Window

Human eyes respond only to wavelengths roughly between 380 nanometres and 750 nanometres. Everything outside this narrow interval remains completely invisible to us without the aid of specialised instruments.

To appreciate how limited this range is, consider that radio waves may extend for several kilometres, while gamma rays may be smaller than the nucleus of an atom. Between these extremes lies an enormous spectrum of invisible radiation, yet evolution has equipped our eyes to detect only the tiny portion most useful for survival on Earth.

Figure 3. The visible spectrum occupies only a tiny portion of the vast electromagnetic spectrum. Human vision is confined to wavelengths between approximately 380 and 750 nanometres, leaving most electromagnetic radiation beyond the reach of our natural senses.

Nature Sees More Than We Do

Perhaps the most remarkable consequence of our limited vision is that other living creatures experience a very different Universe.

Bees can detect ultraviolet patterns on flowers that remain completely invisible to us. Many birds perceive ultraviolet colours as part of their everyday world. Certain snakes can sense infrared radiation emitted by warm prey, effectively allowing them to "see" heat in complete darkness. Mantis shrimps possess one of the most complex visual systems known, with many more types of photoreceptors than humans.

These animals do not inhabit different planets.

They inhabit the same physical world that we do.

Yet each species experiences a different visual reality because evolution has tuned its sensory systems to detect different portions of the electromagnetic spectrum.

The Universe, therefore, is not inherently colourful. It is rich with electromagnetic radiation spanning an enormous range of wavelengths. Every species samples only a small part of that spectrum, and each brain constructs its own version of reality from the information available.

A Humbling Perspective

The next time you look at a beautiful landscape, remember that you are not seeing the whole Universe. You are observing only a tiny, evolutionarily selected slice of reality—a narrow band of electromagnetic radiation that has helped our species survive for hundreds of thousands of years.

Beyond the reds, greens and blues that fill our everyday lives lies an invisible cosmos of radio waves, infrared radiation, ultraviolet light, X-rays and gamma rays. Although our eyes cannot perceive them directly, modern science has developed instruments capable of revealing these hidden worlds, transforming the invisible into knowledge.

The colourful world we experience is therefore not the complete Universe. It is merely one interpretation of a much larger electromagnetic reality.

Now that we understand what light really is, another intriguing question arises.

If the Universe contains only electromagnetic waves, why does a ripe tomato always appear red while fresh leaves appear green? Do objects actually possess colour, or is something else happening at their surfaces?

To answer this, we must examine how light interacts with matter.

Section 4 – Objects Do Not Possess Colour: They Reflect, Absorb and Transmit Light

If the Universe contains only electromagnetic radiation, an obvious question arises.

Why does a ripe tomato always appear red?
Why are leaves green?
Why does the sky look blue?

The answer may surprise you.

Objects themselves do not possess colour.

Instead, every object interacts with the light falling upon it. Some wavelengths are absorbed by the material, some are reflected, some pass straight through, while others may be scattered in different directions. The tiny fraction of light that eventually reaches our eyes is what our brain later interprets as colour.

In other words, an object does not "contain" colour any more than a mirror contains your reflection.

Colour is simply information carried by the reflected light.

How a Red Apple Appears Red

Consider a ripe apple illuminated by ordinary white sunlight.

Sunlight contains a broad mixture of visible wavelengths. When this white light strikes the apple, the pigments within its skin interact with the incoming photons.

Most of the shorter wavelengths—particularly those corresponding to blue and green—are absorbed by the pigments and converted into tiny amounts of heat.

The longer wavelengths are reflected from the surface.

These reflected photons travel towards your eyes, stimulate the cone cells in your retina and are eventually interpreted by your brain as the sensation we call red.

Notice something important.

The apple did not manufacture redness.

It merely reflected certain wavelengths while absorbing others.

The sensation of redness arose only after those reflected wavelengths were processed by your visual system.

Figure 4. A red apple does not contain "redness". Under white illumination, its pigments absorb much of the shorter wavelengths while reflecting predominantly longer wavelengths towards the observer. The sensation of red is created only after these reflected wavelengths are interpreted by the brain.

Different Materials, Different Interactions

Every material possesses its own unique atomic and molecular structure. These microscopic arrangements determine which wavelengths of light are absorbed, reflected or transmitted.

A healthy leaf contains chlorophyll, a pigment that strongly absorbs red and blue wavelengths for photosynthesis while reflecting much of the green portion of the spectrum. Consequently, our brains interpret the reflected light as green.

A ripe banana reflects more of the yellow region of the visible spectrum. Fresh snow reflects nearly all visible wavelengths with roughly equal efficiency, causing it to appear white. Charcoal absorbs most visible wavelengths and reflects very little, so it appears black.

The physical processes occurring within these materials are entirely governed by the interaction between photons and electrons.

At no stage does nature assign colours to the objects themselves.

Colour Depends Upon the Light Source

Perhaps the strongest evidence that objects do not possess fixed colours is that their appearance changes dramatically under different lighting conditions.

A white shirt viewed under midday sunlight appears bright white.

The same shirt illuminated by a candle flame acquires a warm yellow-orange tint.

Under certain coloured LED lights, it may even appear blue, green or pink.

Has the shirt changed?

Of course not.

Only the wavelengths illuminating it have changed.

Since different wavelengths are available for reflection, the information reaching our eyes also changes, prompting the brain to generate a different colour experience.

The Curious Case of a Red Rose

Imagine placing a brilliant red rose inside a room illuminated only with pure blue light.

Since there are virtually no red wavelengths present for the petals to reflect, the rose can no longer appear red. Instead, it may look very dark, grey or even almost black.

The pigments responsible for reflecting red wavelengths are still present.

But without red light falling upon the petals, there is nothing suitable to reflect towards your eyes.

This simple experiment demonstrates that colour depends upon three essential ingredients:

The light source.
The object interacting with that light.
The observer's visual system.

Remove or alter any one of these, and the perceived colour changes.

The Moon Is Another Wonderful Example

When we look at the full Moon with our unaided eyes, it usually appears silvery white or slightly yellow.

In reality, the lunar surface is composed mainly of grey rocks and dust that reflect sunlight rather inefficiently. The subtle mineral colours present on the Moon are so faint that our eyes struggle to perceive them.

Modern digital cameras, however, can accumulate light over longer periods and enhance tiny colour differences through careful image processing. As a result, photographs often reveal delicate bluish, brownish and even reddish regions corresponding to differences in lunar geology.

The colours were always present in the reflected light.

Our eyes simply could not detect them.

A Fundamental Truth

Objects therefore do not possess colour in the way that they possess mass, shape or chemical composition.

Instead, every object acts as a sophisticated optical filter, selectively absorbing, reflecting, transmitting and scattering different wavelengths of electromagnetic radiation.

The light reaching our eyes carries this information.

Our retina converts it into electrical impulses.

Finally, the brain performs the extraordinary task of transforming these signals into the rich tapestry of colours that fills our everyday lives.

Objects do not wear colours.
They merely shape light.
It is the brain that paints them.

But how exactly does the eye capture this reflected light? What remarkable biological sensors enable us to detect wavelengths that are themselves invisible?

To answer that question, we must journey into one of the most sophisticated optical instruments ever produced by evolution—the human eye.

When Absence Has a Name

Our journey through colour has revealed an unexpected truth. What we casually describe as "colour" does not exist as an independent physical property of the Universe. It is a perceptual experience created by the brain after interpreting electromagnetic radiation.

Surprisingly, colour is not the only concept that everyday language treats differently from physics.

Several familiar words describe not the presence of something, but rather its absence.

Consider these common expressions:

"It is cold today."
"Please switch on the light; it is dark."
"The room is completely silent."

These statements feel perfectly natural, yet science interprets them in a subtly different way.

Cold Is the Absence of Heat

In physics, heat is real. It is the transfer of thermal energy arising from the random motion of atoms and molecules.

When an object loses thermal energy, its atoms and molecules move more slowly. We describe this lower thermal energy as cold.

There are no particles of cold flowing into your hands when you touch an ice cube.

Instead, thermal energy leaves your warmer hand and flows into the colder ice until both gradually approach the same temperature.

Your nervous system interprets this outward flow of heat as the sensation of cold.

Darkness Is the Absence of Light

The same principle applies to darkness.

Light consists of photons travelling through space. When these photons reach your eyes, you perceive an illuminated world.

If the photons are absent or too few to stimulate your retina, your brain perceives darkness.

Darkness does not stream into a room when the Sun sets.

No particles of darkness flow through the air.

Darkness is simply the condition in which little or no visible light reaches your eyes.

Silence Is the Absence of Sound

Sound is produced by vibrating objects creating pressure waves that travel through air, water or solids.

When those pressure waves are absent, we experience silence.

Silence is not a physical substance. It is the absence of detectable sound.

Shadow Is the Absence of Light

A shadow is not a dark object cast upon the ground.

It is simply a region where an opaque object blocks light from reaching a surface.

Move the object away, and the shadow instantly disappears—not because it has travelled elsewhere, but because light once again fills that region.

Vacuum: A Note of Scientific Caution

We often describe a vacuum as the absence of matter, and for many everyday purposes this description is entirely adequate.

Modern physics, however, tells us that even the emptiest regions of space are not perfectly empty. Quantum fields permeate the Universe, and fleeting quantum fluctuations can occur even in what we call a vacuum.

Thus, a vacuum is better understood as a region containing extremely little matter rather than absolute nothingness.

A Common Thread

These examples reveal a fascinating pattern in the way science views the natural world.

Everyday Word	Scientific Interpretation
Colour	A perception created by the brain from electromagnetic radiation.
Cold	A state of relatively low thermal energy.
Darkness	The absence of visible light.
Silence	The absence of detectable sound waves.
Shadow	A region where light is blocked.

Science often reveals that the world is simpler—and more elegant—than our everyday language suggests.

The Universe contains matter, energy and the laws of physics.

Our minds enrich that Universe with experiences, sensations and names.

Sometimes what we call a "thing" is, in reality, a perception.
Sometimes it is simply an absence.

Section 5 – Colour Was Never in the Light

By now, we have uncovered a remarkable truth about the physical Universe.

Light travels through space as electromagnetic radiation. Objects selectively absorb, reflect, scatter or transmit different wavelengths of that radiation. Yet nowhere along this journey does colour itself appear.

The Sun does not emit colours.

Space does not carry colours.

Photons do not possess colours.

Even the objects around us are not intrinsically coloured. They merely interact with light according to the arrangement of their atoms and molecules.

If we could somehow freeze a beam of sunlight travelling through the vacuum of space and examine it under a microscope, we would find no traces of red, blue, green or yellow hidden within it. We would observe only electromagnetic waves—or, from the perspective of quantum physics, photons carrying specific amounts of energy.

At this stage of our journey, we have arrived at an intriguing paradox.

The Universe contains light.
Yet we experience colour.

Somewhere between the arrival of photons at our eyes and our conscious awareness of the world, something extraordinary must be happening.

Nature has evolved an instrument capable of detecting tiny differences in wavelength with astonishing precision. It converts invisible electromagnetic radiation into electrical signals, transmitting billions of pieces of information to one of the most complex structures known in the Universe—the human brain.

That remarkable instrument is the human eye.

Far from being a simple camera, the eye is a sophisticated biological detector. It captures only a tiny fraction of the electromagnetic spectrum, converts photons into electrical impulses and sends them along the optic nerve for further processing.

However, the eye itself does not perceive colour.

Its role is to detect light.

The interpretation comes later.

This distinction is crucial.

If the eye were responsible for colour, then removing the eye would remove colour entirely. Yet modern neuroscience has shown that the retina merely begins the process. The signals it generates undergo extensive processing within several specialised regions of the brain before we finally experience the rich world of colours that surrounds us.

The colourful Universe we take for granted is therefore not simply observed—it is actively constructed.

Before we can understand how the brain performs this extraordinary feat, we must first explore the remarkable biological instrument that gathers the raw information.

Our next destination is the human eye—an organ that has fascinated philosophers, artists and scientists for centuries, and one that remains among the most sophisticated optical systems produced by evolution.

Figure 5. The journey from light to colour. Electromagnetic radiation enters the eye, where it is converted into electrical signals. These signals are then processed by the brain, giving rise to the conscious experience of colour. Light is a physical phenomenon; colour is a neurological perception.

The Universe sends light.
The eye detects it.
The brain paints it.
That painting is the colourful world we experience every day.

PART II
The Human Eye – Nature's Extraordinary Light Detector

To understand colour, we must first understand the remarkable instrument that collects the light.

PART II
The Human Eye – Nature's Extraordinary Light Detector

"The eye does not create colour. Its remarkable task is to capture light with extraordinary sensitivity and deliver that information to the brain."

Section 6 – The Human Eye: Nature's Extraordinary Light Detector

If the Universe speaks the language of light, then the human eye is one of nature's finest instruments for listening to that language.

For thousands of years, philosophers regarded the eye with awe. Artists celebrated it as the window to the soul. Today, science recognises it as one of evolution's greatest engineering achievements—a living optical instrument capable of detecting individual photons under favourable conditions while simultaneously operating across an enormous range of brightness.

Yet remarkable as it is, the eye has one important limitation.

It does not see colour.

Instead, its primary task is far more fundamental: to collect light, focus it with exquisite precision, convert it into electrical signals and transmit those signals to the brain.

Everything we eventually perceive—colour, shape, depth, motion and detail—begins with this remarkable biological detector.

A Living Camera—Yet Far More Sophisticated

The eye is often compared with a camera, and the comparison is useful up to a point.

Both possess a lens to focus incoming light. Both regulate the amount of light entering through an adjustable opening. Both project an image onto a light-sensitive surface.

The similarities are summarised below.

Camera	Human Eye
Lens	Cornea & Lens
Aperture	Pupil controlled by the Iris
Image Sensor	Retina
Processor	Brain

The analogy, however, soon reaches its limits.

Unlike a camera, the eye is alive. It constantly changes focus, adjusts to different lighting conditions, repairs minor damage, moves several times every second and collaborates with the brain to construct a coherent picture of the world.

Indeed, what we call "vision" is not produced by the eye alone. It is the result of continuous cooperation between the eye and the brain.

The Journey Begins

Every visual experience begins when photons reflected from an object enter the eye through the transparent outer surface known as the cornea.

The cornea performs most of the eye's focusing, bending the incoming light rays towards the interior of the eye.

The light then passes through the pupil, the dark circular opening that appears in the centre of the iris.

Contrary to popular belief, the pupil is not a black disc. It is simply an opening through which light enters the eye.

Surrounding the pupil is the coloured iris. Tiny muscles within the iris continually adjust the size of the pupil, allowing more light to enter in darkness and restricting excessive light during bright conditions.

Behind the pupil lies the eye's flexible crystalline lens.

Small muscles alter the shape of this lens throughout the day, enabling us to focus on nearby books one moment and distant mountains the next—a process known as accommodation.

Finally, the focused light reaches the retina, a delicate layer lining the back of the eye. It is here that one of biology's greatest transformations takes place.

Light becomes electricity.

Figure 6. Simplified cross-section of the human eye. Light enters through the cornea, passes through the pupil and lens, and is focused onto the retina. The retina converts light into electrical impulses, which travel to the brain through the optic nerve.

The Eye Does Not See

Perhaps the most surprising fact about vision is this:

The eye itself does not "see."

It functions as a highly sophisticated detector, much like the sensor in a scientific instrument. Its job is to gather photons, measure their properties and convert them into electrical signals.

Those signals possess no colours, no beauty and no meaning by themselves.

Meaning arises only when billions of neurons within the brain begin interpreting the incoming information.

The eye supplies the data. The brain constructs the experience.

To appreciate this extraordinary transformation, we shall now accompany a single photon on its remarkable journey—from the surface of an object to the deepest regions of the human visual system.

Section 7 – The Remarkable Journey of a Single Photon

Every visual experience begins with an extraordinarily small traveller—a single photon.

Photons are the smallest discrete packets, or quanta, of electromagnetic radiation. They possess no mass at rest, carry energy and momentum, and travel through the vacuum of space at the universal speed of light, approximately 299,792 kilometres per second (186,282 miles per second).

Every second, trillions upon trillions of these tiny messengers enter our eyes. Most complete their journey unnoticed. Others become part of one of the greatest transformations in nature—the conversion of light into thought.

A Journey That Began Eight Minutes Earlier

Imagine looking at a fresh green leaf on a bright sunny morning.

The photons entering your eye at this very moment began their journey nearly eight minutes and twenty seconds earlier at the surface of the Sun, almost 150 million kilometres away.

Born within the Sun's blazing photosphere, they travelled through the vacuum of interplanetary space before finally reaching Earth.

When those photons struck the surface of the leaf, an important interaction occurred.

The chlorophyll molecules absorbed much of the red and blue portions of the incoming sunlight for photosynthesis, while much of the green wavelengths were reflected back into the surrounding environment.

One of those reflected photons now begins its final journey towards your eye.

Figure 7. A photon begins its journey at the Sun, interacts with the leaf and finally enters the human eye carrying information about the leaf's surface. The photon itself is not green; the sensation of green will emerge only after the brain interprets the signals generated by the retina.

Entering the Eye

The reflected photon first encounters the transparent cornea, where it begins to bend towards the optical axis of the eye. Passing through the aqueous humour, it enters the pupil, whose diameter is constantly adjusted by the iris according to ambient lighting conditions.

Next, the photon passes through the crystalline lens. Tiny muscles attached to the lens continually alter its shape, ensuring that the incoming light is focused sharply onto the retina.

Within only a fraction of a second, the photon reaches the back of the eye.

Its journey through space is over.

An even more remarkable journey is about to begin.

When Light Becomes Electricity

The retina is lined with millions of specialised photoreceptor cells that are capable of detecting incoming photons with extraordinary sensitivity.

When our photon strikes a suitable photoreceptor, it is absorbed by a light-sensitive pigment molecule. This single interaction triggers an intricate biochemical cascade involving proteins, enzymes and ion channels.

Within an astonishingly short time, the photon's energy has been transformed into an electrical signal.

The photon itself no longer exists.

Its energy has been absorbed.

Its journey has ended.

Yet the information it carried continues travelling through the nervous system.

A Signal Begins Its Journey

The newly generated electrical impulse is relayed through several layers of retinal neurons, including bipolar cells, horizontal cells, amacrine cells and finally ganglion cells.

The long fibres of the ganglion cells gather together to form the optic nerve, carrying millions of electrical impulses towards the brain every second.

Remarkably, the information travelling along the optic nerve is still not "colour."

It consists only of patterns of electrical activity—tiny voltage changes travelling along nerve fibres.

Somewhere deep within the brain, these electrical patterns will eventually become the vivid experience of green leaves, blue skies, colourful flowers and brilliant sunsets.

The transformation has not yet occurred.

The brain has not yet begun to paint.

An Extraordinary Thought

Every object you have ever seen has been built from countless journeys like this.

Every smile you have recognised, every page you have read, every painting you have admired and every distant galaxy you have observed has depended upon innumerable photons completing similar voyages from their source to your retina.

Each photon carries only a minute fragment of information.

Collectively, they allow your brain to construct an entire Universe.

The photon never carried colour.
It carried information.

The eye never created colour.
It created electrical signals.

Only the brain will transform those signals into the colourful reality we experience every day.

To understand how this remarkable transformation begins, we must now examine the retina itself—a living sheet of neural tissue where light is first converted into electrical language.

Section 8 – The Retina: Where Light Becomes Electricity

If the cornea, iris and lens are the optical components of the eye, then the retina is its living detector. Hidden at the back of the eyeball lies one of the most extraordinary biological structures known to science—a remarkably thin layer of nervous tissue that transforms invisible electromagnetic radiation into the electrical language of the brain.

Although only about 0.2 millimetres thick, the retina contains millions of highly specialised cells working together with astonishing precision. Every visual experience begins here. Before the brain can recognise a face, admire a sunset or appreciate a painting, the retina must first convert incoming photons into electrical signals.

Unlike the sensor in a digital camera, the retina is alive. It does not simply record an image. It analyses, filters, enhances and compresses visual information before transmitting it to the brain.

In many respects, the retina performs the first stage of image processing long before conscious vision begins.

The Retina Is Actually Part of the Brain

One of the most fascinating facts about human anatomy is that the retina is not merely attached to the brain—it is actually an extension of it.

During embryonic development, the retina forms directly from the developing brain and remains connected throughout life by the optic nerve. This means that when light enters the eye, it encounters living nervous tissue almost immediately.

The retina is therefore not simply a light-sensitive surface. It is neural tissue performing complex computations in real time.

Long before electrical signals reach the visual cortex, the retina has already begun interpreting brightness, contrast, edges and movement.

Figure 8. A simplified representation of the retina. Incoming light is detected by photoreceptors, converted into electrical signals and relayed through bipolar and ganglion cells before travelling to the brain via the optic nerve.

From Photons to Electrical Signals

The retina contains two principal types of light-sensitive cells known as photoreceptors. These are the cells that directly interact with incoming photons.

When a photon strikes a photoreceptor, it is absorbed by specialised pigment molecules. This initiates an intricate chain of biochemical reactions known as phototransduction.

During this process, the energy carried by the photon is converted into tiny electrical changes across the cell membrane.

Remarkably, this conversion occurs with extraordinary efficiency. Under ideal conditions, the human visual system is so sensitive that a rod cell may respond to only a handful of photons.

Nature has evolved an optical detector of astonishing performance—one that engineers continue to study and admire.

The Retina Is More Than a Sensor

Many people imagine that the retina behaves like photographic film or the sensor inside a smartphone camera.

In reality, it is far more sophisticated.

The retina performs significant processing before information ever reaches the brain. Networks of specialised neurons compare neighbouring regions of the image, emphasise edges, suppress visual noise, adapt to changing illumination and improve contrast.

This means that the signals travelling along the optic nerve are not raw copies of the outside world. They have already been analysed and refined.

Modern digital image processing uses algorithms to sharpen photographs, reduce noise and enhance contrast.

The retina has been performing similar operations for hundreds of millions of years.

The Blind Spot

One of the retina's most intriguing features is that it contains a small region where there are no photoreceptors at all.

This region, known as the optic disc, is where the optic nerve exits the eye to carry visual information towards the brain.

Because no rods or cones are present there, every human eye possesses a natural blind spot.

Yet under normal circumstances we never notice it.

The reason is remarkable.

The brain automatically fills in the missing information using data from the surrounding retina and the other eye. Once again, our visual experience is not a direct recording of reality but an intelligent reconstruction.

The Fovea — The Centre of Sharp Vision

Near the middle of the retina lies a tiny depression called the fovea. Although only a few millimetres across, it is responsible for our sharpest vision.

Whenever you read this sentence, recognise a familiar face or admire the intricate details of a flower, you are directing the image onto the fovea.

This small region contains an exceptionally high concentration of cone cells and is largely responsible for our ability to perceive fine detail and vivid colour under good lighting conditions.

Outside the fovea, visual sharpness gradually decreases, although peripheral vision becomes much more sensitive to movement and low light.

The Beginning of Perception

By the time electrical signals leave the retina through the optic nerve, an extraordinary transformation has already taken place.

The photons that entered the eye no longer exist. Their energy has been absorbed and converted into electrical impulses travelling through living neurons.

Yet these impulses are still not colours.

They are patterns of electrical activity—coded messages awaiting interpretation.

The next stage of our journey introduces the remarkable cells that make vision possible under both brilliant daylight and the faintest starlight.

These are the retina's two great specialists: the rods and the cones.

The retina does not see colours.
It converts light into electricity.

The brain will later transform those electrical signals into the colourful world we experience.

Section 9 – Rods and Cones: The Two Guardians of Human Vision

If the retina is the eye's living detector, then its true heroes are two remarkable types of photoreceptor cells known as rods and cones. Working together, these microscopic cells allow us to navigate a world that ranges from dazzling midday sunshine to the faint glow of distant stars.

At first glance, rods and cones appear to perform similar tasks—they both detect incoming light. Yet evolution has assigned them very different responsibilities. One excels in darkness, the other in daylight. One sees the world largely without colour, while the other paints our universe with vivid hues.

Together, they provide one of nature's most elegant engineering solutions.

How Many Do We Have?

The human retina contains approximately 120 million rods and about 6 million cones. In other words, rods outnumber cones by roughly twenty to one.

This overwhelming dominance reflects an important evolutionary fact. For much of our evolutionary history, survival depended more upon detecting movement and navigating under poor lighting than appreciating the colours of flowers or paintings.

Nature therefore invested heavily in highly sensitive rod cells.

Figure 9. The retina contains far more rods than cones. Rods provide exceptional sensitivity under dim conditions, whereas cones enable colour vision and high-resolution daylight vision.

Rod Cells – Masters of Darkness

Rod cells are among the most sensitive light detectors found in nature. They can respond to extraordinarily small amounts of light, making them indispensable during twilight, moonlit nights and astronomical observations.

However, this remarkable sensitivity comes with a limitation.

Rod cells cannot distinguish colours.

Instead, they simply measure the intensity of incoming light. The information they send to the brain resembles a highly sensitive black-and-white photograph.

This explains a familiar experience.

Walk into a dimly lit room and colours gradually begin to fade. Red flowers lose their brilliance, green leaves become greyish, and blue objects appear increasingly colourless.

The colours have not disappeared.

Rather, the illumination has fallen below the level required for the cone cells to function effectively. Rods now dominate vision, producing a largely monochromatic view of the world.

Cone Cells – Artists of Daylight

Cone cells require considerably brighter illumination than rods, but they reward us with two extraordinary abilities: fine detail and colour perception.

These cells are concentrated within the fovea—the small central region of the retina responsible for our sharpest vision.

Whenever you read a book, admire a painting or recognise a familiar face, your eyes automatically position the image upon this tiny cone-rich region.

Unlike rods, cones exist in three principal varieties, each responding most strongly to different regions of the visible spectrum.

They are commonly referred to as:

Short-wavelength (S) cones — most sensitive to blue light.
Medium-wavelength (M) cones — most sensitive to green light.
Long-wavelength (L) cones — most sensitive to yellow-red light.

It is the combined activity of these three cone types that enables the brain to construct the millions of colours we experience every day.

Why Stars Appear Grey

One of the most fascinating consequences of rod-dominated vision becomes apparent beneath a dark night sky.

To the unaided eye, most stars appear white, bluish-white or faintly yellow. Bright planets may show subtle colours, but galaxies, nebulae and many star clusters often appear as delicate grey smudges.

This is not because these celestial objects lack colour.

In reality, many nebulae glow brilliantly in reds, blues and greens due to the emission of specific wavelengths by excited gases. The famous Orion Nebula, the Lagoon Nebula and countless others are spectacularly colourful when photographed.

The problem lies not in the objects themselves, but in our eyes.

The light reaching our retinas from these distant wonders is simply too faint to activate our cone cells efficiently. Rods take over, providing only brightness information.

Our brains therefore receive almost no colour data to interpret.

The Universe has not become colourless.

Our visual system has merely switched operating modes.

Astronomers and Averted Vision

Experienced amateur astronomers rarely look directly at extremely faint galaxies or nebulae.

Instead, they employ a technique known as averted vision.

By looking slightly to one side of a faint object rather than directly at it, the image falls upon regions of the retina containing many more rod cells.

The object often appears brighter and easier to detect.

Although this may seem counter-intuitive, it is one of the oldest and most valuable observing techniques in astronomy.

Figure 10. Averted vision. Looking slightly away from a faint astronomical object causes its image to fall on rod-rich regions of the retina, improving detectability under dark skies.

Nature's Perfect Partnership

Rather than relying upon a single type of detector, evolution equipped humans with two complementary visual systems.

Rod cells provide extraordinary sensitivity when light is scarce.

Cone cells deliver colour, sharpness and fine detail when light is abundant.

The brain seamlessly combines information from both systems, allowing us to experience a visual world that is both remarkably sensitive and astonishingly colourful.

Rods reveal that something is there.

Cones reveal what it looks like.

Together, they allow the brain to transform light into the rich visual world we experience every moment of our lives.

Yet one profound question remains.

If rods see only shades of grey, and cones merely measure different wavelengths of light, where do the colours themselves finally appear?

The answer lies not in the eye—but within the extraordinary neural networks of the human brain.

Section 10 – Why the Night Sky Loses Its Colours

Have you ever wondered why photographs of the night sky are filled with breathtaking colours, while the same celestial objects often appear grey or faintly white through the eyepiece of a telescope?

The answer lies not in the stars, galaxies or nebulae.

It lies within our own eyes.

One of the greatest surprises awaiting every amateur astronomer is discovering that the magnificent colours seen in modern astrophotographs are genuinely present in the light arriving from space. The camera has not invented them. Instead, it has patiently collected enough photons to reveal colours that our own eyes cannot detect under extremely faint illumination.

Night Vision Belongs to the Rods

As daylight fades, the amount of light reaching the retina steadily decreases. Cone cells, which are responsible for colour vision, require relatively bright illumination to function effectively.

Once the light level falls below a certain threshold, the cones gradually become less active, and the far more sensitive rod cells take over.

Rod cells are extraordinarily efficient at detecting faint light.

However, they possess one significant limitation.

They cannot distinguish colours.

Instead, they measure only the brightness of incoming light.

Consequently, the night sky slowly transforms into a world dominated by shades of grey.

This is why a white building under moonlight, a distant mountain and even your own surroundings often appear almost monochromatic despite retaining all their daytime colours.

The Orion Nebula — A Wonderful Example

One of the finest demonstrations of this phenomenon is the magnificent Orion Nebula.

Viewed through a small telescope under dark skies, the Orion Nebula appears as a delicate glowing cloud, often grey with perhaps the slightest hint of green to experienced observers using larger instruments.

Yet long-exposure photographs reveal an astonishing spectacle of crimson hydrogen clouds, bluish reflection nebulae and subtle green emissions from ionised oxygen.

Has the camera added these colours?

No.

Those colours were always present in the incoming light.

The human eye simply could not gather enough photons within the brief instant of normal vision for the cones to respond effectively.

The camera, by collecting light for many seconds or even hours, accumulates sufficient information for those colours to emerge.

Figure 11. The same nebula viewed by the human eye and by a long-exposure camera. The eye detects only a small fraction of the available light, whereas the camera accumulates photons over time, revealing colours that are genuinely present in the incoming radiation.

The Moon Is Not Truly Grey

To the unaided eye, the Moon appears largely grey or silvery white.

However, the lunar surface contains subtle variations in mineral composition. Different regions reflect sunlight in slightly different ways, producing delicate bluish, brownish and tan hues that are almost impossible for our eyes to perceive directly.

Modern digital photography can enhance these extremely small colour differences, revealing the geological diversity of the lunar surface without altering its scientific authenticity.

Once again, the colours were always there.

Our eyes simply lacked the sensitivity to appreciate them.

Galaxies Are Rich in Colour Too

The same principle applies to distant galaxies.

When viewed through amateur telescopes, most galaxies appear as soft grey patches of light. Yet photographs reveal glowing yellow central bulges, bluish spiral arms filled with young stars, reddish clouds of hydrogen gas and dark lanes of cosmic dust winding gracefully through their discs.

The apparent absence of colour is therefore not a property of the galaxies themselves.

It is a limitation imposed by our own visual system.

The Camera Has a Superpower

Unlike the human eye, a digital camera is not limited to collecting light for only a fraction of a second.

Its electronic sensor can continue accumulating photons for many seconds, minutes or even hours.

Every additional photon improves the signal recorded by the sensor. Extremely faint colours that remain invisible during ordinary vision gradually become measurable.

This explains why astrophotographers often spend entire nights capturing dozens or even hundreds of individual exposures before combining them into a single image.

The resulting photograph is not creating colours that never existed.

Rather, it is patiently revealing colours that were always present but too faint for human perception.

A Universe Far Richer Than Our Eyes

Perhaps the greatest lesson astronomy teaches us is one of humility.

The night sky we experience with our unaided eyes is not the complete Universe.

It is merely the tiny portion that our biological vision can detect under the available illumination.

Beyond the grey glow of nebulae and galaxies lies an astonishing cosmos rich in reds, blues, greens, violets and countless subtle shades that our eyes seldom have the opportunity to perceive directly.

Modern astronomy does not create this hidden beauty.

It reveals it.

The Universe never lost its colours.

Our eyes simply stopped collecting enough light to see them.

Yet another mystery remains.

If rod cells see only brightness and cone cells merely detect different ranges of wavelengths, where does the sensation of colour finally emerge?

The answer takes us beyond the eye and into the most extraordinary image-processing system known—the human brain.

PART III
The Brain Paints the Universe

"The eye gathers light.
The brain transforms it into reality."

Section 11 – The Brain Paints the Universe

We have now reached perhaps the most astonishing discovery in our journey.

Light itself possesses no colour. Objects do not possess colour. The eye does not perceive colour. Even the retina merely converts light into electrical impulses.

So where does colour finally appear?

Inside the human brain.

Everything you have ever seen—the deep blue of the ocean, the brilliant red of a rose, the emerald green of a forest, the golden glow of a sunset and the delicate colours of distant nebulae—exists as a conscious experience created by billions of neurons working together inside your brain.

The colourful universe we experience every day is therefore not projected onto the retina. It is reconstructed inside the mind.

Electricity Has No Colour

After photons strike the retina, they are converted into tiny electrical impulses travelling along the optic nerve.

These impulses are remarkably simple.

They consist only of changing electrical voltages generated by nerve cells.

There are no red electrical signals. There are no blue electrical signals. There are no green electrical signals.

Every impulse travelling through the optic nerve is fundamentally the same kind of electrical event.

The only differences lie in:

which neurons are firing,
how frequently they fire,
how strongly they respond, and
the complex patterns they form.

The brain analyses these patterns with astonishing speed, eventually constructing what we consciously experience as colour.

The Visual Cortex — Nature's Image Processor

The electrical signals leaving the retina first travel through the optic nerve before reaching a relay station deep within the brain called the lateral geniculate nucleus (LGN) of the thalamus.

From there, the information is transmitted to the primary visual cortex, situated in the occipital lobe at the back of the brain.

This is where visual processing truly begins.

Far from simply displaying an image like a television screen, the visual cortex performs an extraordinary amount of computation.

Different groups of neurons specialise in analysing different aspects of the incoming information.

Some detect edges.
Some detect movement.
Some analyse orientation.
Some recognise depth.
Some compare colours.
Others identify familiar faces and objects.

These processes occur simultaneously and unconsciously, allowing us to perceive a seamless world.

Figure 12. Light is transformed into electrical signals by the eye. These signals travel through the optic nerve to specialised regions of the brain, where the conscious experience of colour finally emerges.

The Brain Constantly Corrects Reality

Perhaps even more remarkable is that the brain does not simply accept the information arriving from the eyes.

It continuously edits, corrects and improves it.

It compensates for changing illumination.

It removes the blind spot present in every eye.

It stabilises the image despite the fact that our eyes make tiny movements several times every second.

It estimates depth from two slightly different viewpoints.

It recognises familiar faces almost instantly.

And it maintains remarkably consistent colours even when the colour of the illumination changes dramatically.

In many respects, vision is less like looking through a window and more like watching an incredibly sophisticated real-time computer simulation generated from incoming sensory information.

Colour Exists Only as Experience

Suppose we could somehow follow a photon from the Sun until it reached your brain.

At no point along its journey would we discover anything physically resembling redness, blueness or greenness.

We would observe electromagnetic radiation.

We would observe molecules absorbing photons.

We would observe electrical signals travelling along neurons.

Only when billions of neurons interact does the conscious experience of colour emerge.

Colour therefore belongs neither to light nor to objects.

It belongs to perception.

A Symphony Rather Than Individual Notes

An orchestra provides a useful analogy.

A single violin note does not constitute a symphony. Neither does a single trumpet or drumbeat.

Only when hundreds of instruments perform together under careful coordination does music emerge.

Likewise, no individual neuron contains the colour red. No single brain cell stores the experience of blue.

Colour emerges from the coordinated activity of immense networks of neurons working together with astonishing speed and precision.

In neuroscience, this is known as an emergent property—a phenomenon that arises from complex interactions but cannot be found within any single component alone.

Reality as the Brain Constructs It

This does not mean that the external world is an illusion. Photons, atoms, molecules and electromagnetic radiation are all physically real.

However, the colourful world we consciously experience is the brain's remarkably successful interpretation of those physical signals.

Evolution did not shape our brains to reveal reality exactly as it is.

Instead, it shaped them to produce a useful representation of reality—one that enhances survival, allows rapid decision-making and enables us to navigate an extraordinarily complex world.

The Universe provides light.

The retina converts it into electricity.

The brain transforms that electricity into colours, shapes, beauty and meaning.

The colourful world you experience has never existed outside your mind exactly as you perceive it.

Yet another fascinating mystery remains.

If humans construct colours inside the brain, do all humans construct exactly the same colours?

Surprisingly, the answer is no.

Some people can distinguish significantly more colours than others, while millions cannot perceive certain colours at all.

To understand why, we must next explore the remarkable diversity of human colour vision.

Section 12 – Do We All See the Same Colours?

Imagine standing beside another person and both of you looking at the same beautiful rainbow.

The red band appears brilliant. The green looks vibrant. The violet seems deep and mysterious.

It feels natural to assume that both of you are experiencing exactly the same colours.

Surprisingly, science cannot guarantee that.

Although two healthy people may use the same colour names, the colours constructed inside their brains may not be identical.

Each person's visual system is shaped by genetics, biology, age and even subtle differences in the wiring of the brain.

In other words, every one of us experiences a slightly different visual universe.

Three Types of Cone Cells

As we learnt in the previous section, normal human colour vision depends upon three different types of cone cells.

Each responds most strongly to a different region of the visible spectrum:

S-cones – most sensitive to shorter wavelengths (blue).
M-cones – most sensitive to medium wavelengths (green).
L-cones – most sensitive to longer wavelengths (yellow-red).

The brain continuously compares the responses of these three cone types.

From those comparisons emerges the astonishing richness of human colour perception.

Remarkably, this three-channel system allows us to distinguish several million different colours under favourable viewing conditions.

Women Often Distinguish More Colours

One of the most fascinating discoveries in vision science concerns differences between male and female colour perception.

On average, women tend to distinguish slightly finer differences between similar colours than men.

This does not mean that every woman sees more colours than every man.

Rather, statistical studies have shown that women generally perform better in tasks involving subtle colour discrimination, particularly among closely related shades.

Many artists, designers, textile specialists and colour professionals have long observed this tendency, and modern vision science offers an explanation rooted in genetics.

The Genetics Behind Colour Vision

The genes responsible for producing the red-sensitive and green-sensitive visual pigments are located on the X chromosome.

Women possess two X chromosomes (XX), whereas men possess one X and one Y chromosome (XY).

Because women carry two copies of these colour vision genes, they may inherit slightly different versions from each parent.

In most women, the brain combines these inputs into normal trichromatic vision.

In a very small proportion of women, however, an extraordinary situation may arise.

The Rare World of Tetrachromacy

Some women possess four functionally distinct classes of cone photoreceptors instead of the usual three.

This condition is known as tetrachromacy.

Whereas most humans compare signals from three cone types, a tetrachromat has the potential to compare information from four independent channels.

In theory, this greatly increases the number of colour differences that can be distinguished.

Imagine listening to music with an additional instrument that no one else can hear.

The melody remains recognisable to everyone, yet the overall experience becomes richer and more detailed.

Colour perception in tetrachromats may be somewhat similar.

Research suggests that some tetrachromatic women can distinguish colour differences that appear completely identical to most other people.

Scientists continue to investigate exactly how common functional tetrachromacy is, but it is considered relatively rare.

Figure 13. Most humans are trichromats, possessing three classes of cone photoreceptors. A small proportion of women may possess four functionally distinct cone types, a condition known as tetrachromacy, potentially enabling finer colour discrimination.

Not Everyone Sees the Same Rainbow

Even among people with perfectly normal vision, no two brains are wired in precisely the same way.

Each brain develops through a unique combination of genetics, life experiences and neural connections.

Consequently, the precise subjective experience of colour remains deeply personal.

Philosophers sometimes ask an intriguing question:

Is the red that you experience the same red that I experience?

Science cannot answer this question directly because colour is a private conscious experience.

We can measure wavelengths with extraordinary precision. We can record neural activity. We can compare behaviour.

But the subjective experience itself exists only within each individual mind.

Nature Celebrates Diversity

The remarkable diversity of human colour vision reminds us that there is no single, universal way of experiencing the visual world.

Some people distinguish extraordinarily subtle differences between shades. Others perceive colours differently because of inherited variations in their cone cells. Many experience perfectly typical trichromatic vision.

Nature has not produced identical observers.

Instead, it has produced billions of unique visual systems, each constructing its own interpretation of the same physical universe.

The rainbow in the sky is the same for everyone.

The rainbow experienced inside each mind may be wonderfully unique.

Yet there are people whose colour vision differs far more dramatically.

Millions of individuals cannot distinguish certain colours at all—a condition commonly known as colour blindness.

Understanding why this occurs provides another fascinating insight into how our brains construct reality.

Section 13 – When the Brain Paints Differently: Understanding Colour Blindness

If colour exists only as a perception created by the brain, then it follows naturally that any change in the eye's light detectors will change the colours that the brain is able to construct.

This is precisely what happens in people with colour vision deficiency, commonly known as colour blindness.

Despite its popular name, colour blindness rarely means that a person sees the world entirely in black and white.

In reality, most affected individuals perceive colours quite well. They simply have difficulty distinguishing certain combinations of colours because one or more types of cone cells are absent or function differently.

Once again, this reminds us of one of the central themes of this article:

The colours we experience depend not only upon light itself, but also upon the biological equipment through which we observe it.

Why Does Colour Blindness Occur?

As we learnt in the previous section, normal colour vision depends upon three classes of cone cells—S, M and L cones—which respond preferentially to different regions of the visible spectrum.

If one type of cone is missing, damaged or contains an altered visual pigment, the brain receives incomplete information.

It then becomes much more difficult to distinguish certain colours, particularly those whose wavelengths produce similar responses in the remaining cone cells.

The light entering the eye has not changed.

The objects themselves have not changed.

Only the biological interpretation has changed.

The Most Common Types

Scientists classify colour vision deficiencies according to the affected cone cells.

Condition	Cone Affected	Difficulty Distinguishing
Protanopia	L-cones (red)	Red and green shades
Deuteranopia	M-cones (green)	Green and red shades
Tritanopia	S-cones (blue)	Blue and yellow shades
Monochromacy	Most or all cones absent	Little or no colour perception

Red–Green Colour Vision Deficiency

The vast majority of colour vision deficiencies involve difficulty distinguishing red and green hues.

This does not mean that people confuse every red object with every green object.

Instead, certain shades that appear clearly different to most people may look remarkably similar.

For example, ripe fruit among green leaves, coloured electrical wiring, traffic signals viewed from unusual angles, or colour-coded graphs may become difficult to interpret without additional visual cues.

Most people with colour vision deficiency adapt extremely well and often develop alternative strategies using brightness, position, texture and context.

Why Are Men Affected More Often?

One of the most interesting aspects of colour vision deficiency is that it affects men far more frequently than women.

The reason once again lies in genetics.

The genes responsible for the red-sensitive and green-sensitive visual pigments are located on the X chromosome.

Since males possess only one X chromosome (XY), a defective gene on that chromosome is usually enough to produce colour vision deficiency.

Females possess two X chromosomes (XX). If one carries a defective gene, the other often provides a normal copy, greatly reducing the likelihood of developing the condition.

As a result:

Approximately 8% of men (about 1 in 12) have some form of red–green colour vision deficiency.
Only about 0.5% of women (about 1 in 200) are similarly affected.

This striking difference has been recognised for more than a century and remains one of the classic examples of X-linked inheritance in genetics.

Figure 14. A simplified illustration showing how colours that appear clearly distinct to most observers may become difficult to distinguish for someone with a red–green colour vision deficiency. Individual experiences vary depending on the specific type and severity of the condition.

The Ishihara Colour Plates

One of the world's most widely used tests for colour vision was developed by the Japanese ophthalmologist Dr Shinobu Ishihara in 1917.

The famous Ishihara plates consist of hundreds of coloured dots arranged to conceal numbers or patterns.

People with normal colour vision easily recognise the hidden figure, whereas those with certain colour vision deficiencies may see a different number—or none at all.

The test has become a standard screening tool in schools, hospitals, aviation, railways, the armed forces and numerous professions where accurate colour recognition is important.

Colour Blindness Does Not Mean Poor Vision

People with colour vision deficiency generally have perfectly normal eyesight.

They read, drive, study, work, create art, become scientists, engineers, musicians and astronomers.

Their brains simply interpret certain wavelengths differently.

Many individuals remain unaware that they have a colour vision deficiency until they undergo formal testing.

In fact, the diversity of human colour perception reminds us that there is no single universal experience of colour.

A Lesson Beyond Biology

Perhaps the greatest lesson from colour vision deficiency is philosophical rather than medical.

Two people can look at precisely the same object under identical lighting conditions and genuinely experience different colours—not because either is wrong, but because each brain is constructing reality using slightly different biological information.

Nature does not provide one standard visual experience.

Instead, it offers countless variations on the same remarkable theme.

The Universe sends the same photons to everyone.

Yet every brain paints its own version of reality.

If colour is something created entirely within the brain, then an extraordinary question arises.

Can the brain be persuaded to invent colours that do not even exist in the outside world?

Surprisingly, the answer is yes.

Optical illusions reveal that our brains can create colours, brightness and even movement where none actually exist.

In the next section, we shall discover how easily the brain can be fooled—and what these fascinating illusions reveal about the true nature of human perception.

Section 14 – When the Brain Fools Itself: Optical Illusions and Imaginary Colours

Throughout this article we have gradually uncovered a remarkable truth.

Light itself possesses no colour. Objects possess no colour. The retina merely converts photons into electrical signals. The brain constructs the colourful world we experience.

But how reliable is this construction?

Surprisingly, the answer is:

Not nearly as reliable as we imagine.

Every second, your brain makes thousands of educated guesses about the outside world. Most of these guesses are astonishingly accurate, allowing you to navigate safely through life.

Occasionally, however, those guesses are wrong.

When that happens, we experience what scientists call an optical illusion.

An optical illusion is not a defect of vision. It is evidence that the brain is actively interpreting reality rather than merely recording it.

The Brain Is a Prediction Machine

The visual cortex receives an enormous amount of information every second.

Instead of analysing every photon independently, the brain uses experience, probability and surrounding visual information to make rapid predictions.

Normally these predictions are extraordinarily successful.

However, carefully designed images can exploit these shortcuts, revealing how perception is constructed.

Optical illusions therefore offer scientists a fascinating glimpse into the inner workings of the human brain.

Illusion 1 – The Same Grey Appears Different

Our perception of colour depends strongly upon its surroundings.

The two grey squares below are exactly the same shade.

Yet one appears lighter simply because it is surrounded by a darker background.

Figure 15. Both central squares are identical. Your brain interprets them differently because it automatically compensates for surrounding brightness.

The Brain Judges Relationships, Not Absolute Values

The retina faithfully reports the light reaching each point.

The brain then compares neighbouring regions before deciding how bright or dark something appears.

This ability helps us recognise objects under changing lighting conditions but also makes us susceptible to visual illusions.

Illusion 2 – Colours That Do Not Exist

One of the most astonishing discoveries in neuroscience is that the brain can experience colours that are not physically present.

Stare at a bright red object for about thirty seconds and then immediately look at a white wall.

You will briefly see a green image.

Likewise, staring at blue produces yellow, while staring at black may produce white after-images.

These are known as negative after-images.

No coloured light is reaching your eyes from the white wall.

The colours are being generated entirely within your visual system.

Figure 16. Negative after-images arise because the cone cells temporarily adapt to prolonged stimulation. The brain generates complementary colours even though the surface itself remains white.

Illusion 3 – The Famous Blue and Black... or White and Gold Dress?

In 2015, a simple photograph divided millions of people around the world.

Some observers confidently saw a blue-and-black dress. Others were equally certain it was white and gold.

Both groups were sincere. Neither group was hallucinating.

The difference arose because different brains made different assumptions about the colour of the illumination.

Your visual system constantly attempts to discount the colour of ambient lighting.

When those assumptions differ, entirely different colour experiences emerge from exactly the same image.

The famous dress became one of the most remarkable demonstrations that colour is something the brain computes rather than something that simply exists.

Illusion 4 – A Black-and-White Photograph That Appears Coloured

Perhaps the most extraordinary illusion of all is one that perfectly supports the central message of this article.

Scientists have shown that a black-and-white photograph can appear convincingly coloured simply by overlaying extremely thin coloured lines or patterns.

The photograph itself remains fundamentally monochrome.

Very little actual colour information is added.

Yet the brain spreads those tiny colour hints across neighbouring regions, constructing the impression of a fully coloured image.

In other words, the brain finishes a painting that barely exists.

Later in this article, we shall demonstrate this remarkable phenomenon with an illustration that you can experience for yourself.

Illusion 5 – Motion That Doesn't Exist

Some carefully designed images appear to rotate, shimmer or move even though they are perfectly still.

No object is moving. No pixels are changing.

The motion exists entirely inside the brain.

These fascinating illusions arise because different groups of neurons respond at slightly different speeds to brightness, contrast and edges.

Once again, perception is revealed as an active construction rather than a passive recording.

Illusions Reveal the Brain at Work

Far from being tricks or curiosities, optical illusions are among neuroscience's most valuable research tools.

They reveal how the brain estimates depth, compensates for shadows, stabilises vision, predicts movement and reconstructs colours from incomplete information.

Every illusion reminds us of one profound truth:

We do not simply see the world.

We experience the brain's best interpretation of it.

This idea explains one of the greatest revolutions in photography during the nineteenth century.

When photographers first captured the world in black and white, they unknowingly produced images remarkably similar to the way our rod cells naturally perceive faint light.

That remarkable connection between photography, neuroscience and perception will be the subject of our next section.

Section 15 – Why Black-and-White Photography Often Feels More Powerful

Long before colour photography became commonplace, photographers told stories using nothing more than shades of black, white and grey.

Even today, in an age of ultra-high-definition digital cameras capable of reproducing millions of colours, black-and-white photographs continue to possess a timeless beauty and emotional depth that many people find difficult to explain.

Why should an image containing less visual information sometimes feel more expressive?

The answer lies not only in photography but also within the remarkable workings of the human visual system.

Seeing Beyond Colour

Colour is only one component of vision.

Long before the brain decides whether something is red, blue or green, it first determines where objects are, how bright they are, where the edges lie, whether something is moving and how light and shadow define the three-dimensional world.

These fundamental visual cues are largely independent of colour.

When colour is removed from a photograph, our attention is naturally redirected towards these more basic visual elements.

Contrast becomes more striking.
Light and shadow become more dramatic.
Textures become more noticeable.
Facial expressions become more powerful.
Composition becomes more important.

Instead of being distracted by colour, the brain concentrates on form, structure and emotion.

The World of the Rod Cells

Earlier in this article we learnt that rod cells dominate our vision under dim lighting conditions.

Rod cells do not perceive colour. They respond primarily to differences in brightness.

Consequently, during twilight or beneath a star-filled sky, the visual world naturally resembles a monochrome photograph.

Perhaps this explains why black-and-white imagery often feels strangely familiar.

It echoes the way our visual system has evolved to perceive the world whenever light becomes scarce.

Although daylight vision is richly coloured, our nervous system remains exceptionally sensitive to brightness, contrast and shadow.

These qualities continue to carry enormous emotional and survival value.

The Brain Completes the Picture

One of the remarkable characteristics of black-and-white photography is that it encourages the brain to participate more actively.

Without colour information, the visual cortex begins filling in details from memory and experience.

A viewer may instinctively imagine the warmth of a sunset, the green of a forest or the blue of the ocean even though none of these colours actually appear in the photograph.

The brain becomes a silent collaborator with the photographer.

Rather than merely receiving an image, it helps complete it.

Figure 17. Colour photographs communicate through hue as well as brightness, whereas monochrome photographs rely entirely on light, shadow, contrast and texture. The brain naturally emphasises these structural cues when colour is absent.

Great Masters of Monochrome

Many of history's greatest photographs were captured without colour.

From portraits and documentary photography to wartime journalism and scientific imaging, black-and-white photographs have demonstrated that emotional impact depends far more upon composition, timing and light than upon colour itself.

Even today, many photographers deliberately choose monochrome because it removes visual distractions and allows the essential story to emerge with greater clarity.

Perhaps Colour Is Not Always Necessary

This leads to an intriguing thought.

If colour itself is something constructed by the brain, then perhaps black-and-white photography feels powerful because it strips perception back to its most fundamental ingredients.

It reminds us that the foundations of vision are not colour but light.

Before the brain paints the world, it first measures brightness. Before it experiences colour, it detects contrast. Before it appreciates beauty, it first recognises shape.

In this sense, monochrome photography reveals the architecture upon which colour perception is later built.

Black-and-white photography does not remove reality.

It removes one layer of interpretation,
allowing light itself to become the storyteller.

A Childhood Experiment That Never Left Me

This discussion brings back one of my earliest memories of scientific curiosity.

Around forty-four years ago, when I was about six years old, our family owned a black-and-white television set. Colour televisions were still uncommon in many Indian homes, and I had recently learnt—though I no longer remember from where—that the three primary colours of light, Red, Green and Blue (RGB), could combine to produce the colours we see.

Curiosity soon overcame me.

I somehow obtained three transparent coloured sheets—one red, one green and one blue—and carefully placed them over different parts of the television screen.

To my immense excitement, the experiment worked... at least partially.

Certain portions of the black-and-white picture appeared to acquire faint colours. The effect was far from perfect—perhaps only twenty-five percent successful—but to my six-year-old mind it was magical.

Only many years later did I realise why the experiment produced even a limited degree of success.

The television itself remained completely monochrome. It emitted only different levels of brightness.

The coloured transparent sheets selectively filtered that light before it reached my eyes, providing small hints of colour. My visual system then attempted to interpret those altered brightness patterns as a coloured image.

Looking back, I now realise that this simple childhood experiment unknowingly explored one of the central ideas of this entire article:

Colour is not simply received.

It is constructed.

In the next section, we shall explore an even more astonishing demonstration of this remarkable fact—how a completely black-and-white image can appear vividly coloured with the addition of only a few carefully placed coloured lines, allowing the brain to perform the rest of the work.

Section 16 – How a Black-and-White Image Can Appear Full of Colour

By now, we have reached a remarkable conclusion.

Light carries no colour. Objects possess no colour. The eye merely detects wavelengths. The retina converts those wavelengths into electrical signals. The brain constructs the colours we experience.

Now let us perform one final thought experiment—one that beautifully demonstrates just how much of colour exists inside the brain rather than outside it.

Suppose you are shown an ordinary black-and-white photograph.

Nothing unusual. No coloured pixels. No hidden tricks. Simply a greyscale image containing only different levels of brightness.

Now imagine that someone overlays a few extremely thin coloured lines across selected parts of that image.

Something extraordinary begins to happen.

Although almost the entire photograph remains black and white, your brain gradually starts perceiving large coloured regions where virtually no colour information actually exists.

The colours seem to spread naturally across the image.

Yet the photograph itself has barely changed.

The Brain Hates Incomplete Information

The human brain is remarkably efficient.

Instead of analysing every pixel independently, it constantly searches for patterns, continuity and probable explanations.

When only a few reliable colour clues are present, the visual cortex assumes that neighbouring regions probably share similar colours.

It therefore extends, blends and smooths those colours across surrounding areas.

This process happens automatically.

We are completely unaware that our brains are performing this remarkable act of reconstruction.

Colour Filling-In

Neuroscientists refer to this phenomenon as colour filling-in.

The brain does not simply process colour exactly where colour-sensitive cone cells are stimulated.

Instead, specialised neurons combine information about brightness, edges, textures and neighbouring colours to generate a smooth, continuous visual experience.

Rather than seeing isolated coloured points, we perceive complete coloured objects.

Without this remarkable ability, our visual world would appear fragmented and unstable.

Figure 18. This simplified diagram illustrates the principle of colour filling-in. Only small amounts of colour information are provided, yet the visual cortex extends those colour cues across neighbouring regions, producing the perception of a fully coloured scene.

The Demonstration You Will See Below

Immediately following this section, I have included a fascinating visual demonstration.

At first glance, it appears to be an ordinary coloured picture.

Look more carefully.

You will discover that almost the entire image remains black and white. Only a few carefully placed coloured lines have been added.

Nevertheless, your brain rapidly spreads those colours across the image until it appears almost fully coloured.

Even after you become aware of the illusion, it remains surprisingly difficult to "switch off" the brain's interpretation.

Modern Technology Uses the Same Principle

Interestingly, this remarkable property of human vision is exploited in many areas of modern technology.

Image-compression algorithms reduce the amount of colour information that must be stored by recognising that the human eye is far more sensitive to changes in brightness than to fine changes in colour.

Video compression standards, digital television broadcasting and internet image formats often preserve high-resolution brightness information while storing colour information at lower resolution.

To most viewers, the reconstructed image still appears richly coloured because the brain naturally fills in the missing detail.

Engineers are therefore taking advantage of a feature that evolution perfected hundreds of millions of years ago.

One More Step Towards Understanding Reality

This simple demonstration teaches an extraordinary lesson.

Colour is not something painted onto the world.

It is something painted by the brain.

The outside world provides only physical information—different wavelengths and different intensities of light.

Everything else is interpretation.

Sometimes the brain needs only a whisper of colour

to imagine an entire painting.

This raises one final and profound question.

If colour exists only inside the mind, what does the Universe actually look like without an observer?

To explore that question, we must step beyond biology and enter the realms of physics and philosophy, where science meets one of humanity's oldest questions:

What is reality when no one is looking?

Section 17 – Does the Universe Have Colour Without an Observer?

We have now travelled an extraordinary path.

We began with sunlight. We explored wavelengths. We discovered that objects do not possess colour. We learnt how the retina converts light into electrical impulses and how the brain constructs the vivid world we experience.

Now we arrive at perhaps the most profound question of all.

If no conscious observer existed anywhere in the Universe, would colour still exist?

At first glance, the answer may seem obvious. After all, stars would continue shining, flowers would continue reflecting sunlight, and rainbows would still form in falling raindrops.

Yet science asks us to distinguish carefully between the physical world and our experience of it.

The Universe Exists Without Us

Long before the first human beings appeared on Earth, stars were already burning in distant galaxies. Supernovae exploded. Planets formed. Comets travelled through the Solar System. The oceans rose and fell beneath the pull of the Moon.

None of these phenomena depended upon human observation.

The Universe is not waiting for someone to look at it before it begins to exist.

Atoms, molecules, gravity, electromagnetic radiation and the laws of physics operate whether anyone is present to witness them or not.

Reality is not created by our eyes.

Our eyes merely allow us to experience one tiny part of that reality.

But Colour Is Different

Although the physical Universe exists independently of observers, colour belongs to a different category altogether.

Colour is not a property carried by photons. It is not stored inside flowers. It is not painted onto planets.

Colour is a conscious sensation that emerges only when a nervous system interprets incoming light.

Without an observer possessing a suitable visual system, there are still wavelengths of electromagnetic radiation. There are still photons. There is still reflected light.

What no longer exists is the subjective experience we call red, green, blue or violet.

In exactly the same way, a musical score contains patterns of notes. Only when those notes are performed and heard does the experience of music arise.

Likewise, the Universe contains patterns of electromagnetic radiation. Only when those patterns are processed by a visual brain does the experience of colour emerge.

Figure 19. The physical Universe provides light and reflected wavelengths. The conscious experience of colour emerges only after those signals are interpreted by a visual brain.

Different Eyes, Different Universes

This idea becomes even more fascinating when we consider other living creatures.

Many birds possess four types of cone cells and can perceive ultraviolet wavelengths invisible to humans. Bees navigate using ultraviolet patterns on flowers that we cannot see without specialised cameras. Some snakes detect infrared radiation, allowing them to locate warm prey even in complete darkness.

Each species inhabits the same physical Universe. Yet each experiences a different sensory reality.

The Universe itself has not changed. Only the observer has.

This reminds us that our own perception is neither complete nor privileged. It is simply one successful biological solution shaped by evolution.

Reality and Experience

Science therefore distinguishes between two different kinds of truth.

Physical reality exists independently of observers. Wavelengths, photons and electromagnetic fields continue whether anyone is watching or not.
Conscious experience arises only when a brain interprets those physical signals. Colour belongs to this second category.

Confusing these two ideas has often led to misunderstandings in both science and philosophy.

The Universe is objectively real.

Our experience of that Universe is a beautifully constructed interpretation.

A Universe Richer Than Human Vision

Even the visible spectrum represents only a tiny fraction of the electromagnetic spectrum.

Radio waves stretch for kilometres. Gamma rays possess wavelengths smaller than atomic nuclei. Between them lie microwaves, infrared radiation, visible light, ultraviolet radiation and X-rays.

Our eyes detect only a narrow band because that range proved useful during the evolution of life on Earth.

The cosmos is therefore not merely more colourful than we can see.

It is far richer than any human sense can ever directly experience.

The Universe is not coloured.

The Universe is filled with light.

Colour begins only when light meets a mind capable of experiencing it.

One Final Reflection

As we have seen throughout this journey, science often reveals that familiar words conceal extraordinary truths.

Colour is not painted onto the world.

It is painted within us.

The flowers still reflect wavelengths. The stars still radiate light. The rainbow still separates sunlight into its constituent wavelengths.

Yet redness, blueness and greenness come into existence only as living minds transform those wavelengths into conscious experience.

Perhaps this is one of the most beautiful ideas in all of science.

The Universe provides the notes.

The brain performs the symphony.

In our next section, we shall discover that colour is not the only familiar idea that exists in this curious way. Concepts such as cold, darkness, silence and even a vacuum also remind us that nature often gives names not only to what exists, but also to what is absent.

Section 18 – Nature Often Names Absences

As our journey through colour draws to a close, we arrive at an unexpected realisation.

The deeper science investigates nature, the more it reveals that many familiar words do not describe physical objects at all. Instead, they describe conditions, relationships, or even the absence of something else.

Colour turned out to be one such example.

It is not contained within light. It is not stored inside objects. It is not painted upon flowers, mountains or stars.

Rather, it is a conscious experience constructed by the brain from patterns of electromagnetic radiation.

Remarkably, colour is not unique in this respect. Several other concepts that we use every day also describe absences rather than independent physical entities.

Cold Is Not a Substance

On a winter morning we naturally say,

"It is cold today."

The statement is perfectly correct in everyday conversation, yet physics tells a slightly different story.

Heat is a measurable physical quantity. It represents the thermal energy associated with the random motion of atoms and molecules.

When those particles move rapidly, the temperature is higher. When they move more slowly, the temperature is lower.

What we call cold is simply the absence—or more precisely, a lower amount—of thermal energy.

There are no particles of cold flowing into a room. There is no substance called cold. Instead, heat flows from a warmer object towards a cooler one until thermal equilibrium is reached.

In other words, your hands do not receive cold. They lose heat.

Figure 20. Heat naturally flows from a warmer object to a cooler one. We experience this loss of heat as the sensation of cold.

Darkness Is the Absence of Light

Darkness feels almost tangible. It fills empty rooms. It seems to spread across the landscape after sunset.

Yet darkness is not a physical substance travelling through space.

Light consists of photons—real particles carrying electromagnetic energy.

When photons are plentiful, we experience brightness. When photons are absent or greatly reduced, we experience darkness.

Darkness itself does not travel. It possesses no particles. It has no speed.

Sunrise does not chase darkness away. Instead, sunlight fills space with photons, replacing the absence with presence.

Silence Is the Absence of Sound

The same principle applies to sound.

Sound is created by pressure waves travelling through air, water or solids.

When these waves reach our ears, the brain interprets them as speech, music or noise.

When no significant sound waves are present, we describe the environment as silent.

Silence is therefore not a sound in itself. It is simply the absence of detectable sound.

Vacuum Is the Absence of Matter

Outer space is often described as an empty vacuum.

Strictly speaking, a vacuum is a region containing extremely little matter.

Even the best laboratory vacuum is never perfectly empty. Tiny numbers of atoms and molecules remain.

Likewise, interstellar space contains sparse gas, dust particles, cosmic rays and electromagnetic radiation.

Thus, a vacuum is best understood as the near absence of matter rather than an independent substance.

A Shadow Is Not an Object

A shadow may appear to possess shape and movement. It follows us faithfully on sunny afternoons.

Yet a shadow has no material existence.

It is simply a region where an opaque object prevents light from reaching a surface.

Remove the object, and the shadow immediately disappears.

Once again, what appears to be "something" is actually defined by the absence of light.

Figure 21. A shadow is not a physical object. It is a region where light is prevented from reaching a surface.

Language Gives Names to Both Presence and Absence

Human language evolved to describe the world quickly and efficiently rather than with scientific precision.

Consequently, we naturally give names not only to physical entities but also to their absence.

Heat → Cold
Light → Darkness
Sound → Silence
Matter → Vacuum
Illumination → Shadow
Electromagnetic wavelengths interpreted by the brain → Colour

These words are indispensable in everyday life. They allow us to communicate efficiently and intuitively. Yet science reminds us that beneath these familiar expressions lies a deeper physical reality.

A Different Way of Looking at the Universe

Perhaps one of the greatest gifts of science is that it teaches us to see the ordinary with fresh eyes.

A rainbow becomes more than beautiful. It becomes separated wavelengths of sunlight.

A black night becomes the absence of photons reaching our eyes.

A cold breeze becomes heat leaving our skin.

And colour itself becomes one of the brain's greatest masterpieces—a vivid interpretation painted upon a canvas of invisible electromagnetic radiation.

Nature gives us light, heat, sound and matter.

The absence of these also earns names.

Our language speaks of both presence and absence,
while science gently reminds us which is which.

With that understanding, we are finally ready to return to the simple idea that inspired this entire article.

It began with a quiet observation:

"Colour does not exist."

We now understand that the statement is both surprising and profoundly beautiful.

In the final section, we shall gather together everything we have learnt and reflect upon the extraordinary painted dream through which we walk every day.

Section 19 – We Have Been Walking Through a Painted Dream All Along

Every now and then, science presents us with an idea so simple, yet so profound, that once understood, we can never look at the world in quite the same way again.

This journey began with one such idea.

Colour does not exist.

At first, the statement sounds absurd.

After all, the blue sky stretches above us. Leaves are green. Blood is red. The oceans sparkle beneath a golden sunrise. Flowers bloom in countless brilliant shades. The planets, stars and galaxies fill astronomy books with magnificent colours.

Surely colour must be one of the most obvious features of the Universe.

Yet science gently asks us to look deeper.

The Universe Speaks in Wavelengths

Outside our bodies there are no reds, blues or greens floating through space.

There are only electromagnetic waves of different wavelengths travelling at the speed of light.

Flowers do not manufacture redness.

They simply absorb some wavelengths and reflect others.

The evening sky does not become orange because orange exists in the atmosphere.

The atmosphere merely scatters sunlight in ways that allow certain wavelengths to dominate our view.

The Universe itself speaks the language of physics.

Colour is the language our brains use to translate that physics into experience.

The Greatest Artist Lives Inside Our Heads

Throughout this article we have repeatedly encountered the same remarkable truth.

The eye is not a camera.

The retina is not a painting.

The optic nerve carries no coloured signals.

Instead, billions of neurons collaborate continuously, transforming electrical impulses into an astonishingly rich visual world.

Every colour you have ever experienced has been created within the living tissue of your own brain.

In that sense, each of us carries within our skull the most extraordinary artist nature has ever produced.

Without ever holding a paintbrush, it paints the entire Universe.

Reality Is Richer Than Human Vision

Perhaps the most humbling lesson of all is that our colourful world represents only a tiny window into reality.

Our eyes detect only a narrow band of the electromagnetic spectrum.

Beyond red lies infrared radiation. Beyond violet lies ultraviolet. Far beyond both stretch radio waves, microwaves, X-rays and gamma rays.

The Universe is not limited to what we can perceive.

Our senses merely reveal the tiny portion that evolution found useful for survival on Earth.

Astronomers routinely observe invisible wavelengths using specialised telescopes. Only later are those invisible signals translated into colours that our brains can understand.

Ironically, many of the most colourful astronomical images ever produced depict light that no human eye could ever directly see.

Nature Is Simpler Than Our Language

Along the way we also discovered another fascinating lesson.

Colour is not alone.

Cold is the absence of heat.

Darkness is the absence of light.

Silence is the absence of sound.

A shadow is the absence of illumination.

A vacuum is the near absence of matter.

Human language gives names to these absences because they are meaningful in everyday life.

Science gently peels back those familiar words and reveals the elegant simplicity beneath them.

A Memory That Began With Curiosity

Looking back, I now smile at the memory of a six-year-old boy placing red, green and blue transparent sheets over the screen of a black-and-white television, hoping to create colour where none existed.

The experiment was only partially successful.

Yet perhaps it succeeded in a far more important way.

It planted a question that remained quietly alive for decades.

How does colour really come into existence?

Science eventually provided the answer.

Not with magic. Not with mystery. But with something even more beautiful—understanding.

The Painted Dream

Every morning we open our eyes and instantly find ourselves immersed in a brilliant world of colours.

The experience feels so immediate, so effortless and so convincing that we rarely pause to wonder how it is possible.

Yet behind that effortless experience lies one of nature's greatest achievements.

Photons that have travelled for mere nanoseconds from a nearby flower—or for millions of years from a distant galaxy—enter the eye.

Within fractions of a second they are transformed into electrical signals.

Those signals race through intricate networks of neurons until, somehow, conscious experience emerges.

Red appears. Blue appears. Green appears. Beauty appears.

Not because the Universe contains those experiences...

...but because the human brain creates them.

One Final Thought

Science does not make the world less beautiful.

It makes it infinitely more astonishing.

To know that colours are not painted upon the Universe but painted within ourselves does not diminish a rainbow.

It transforms that rainbow into one of the greatest collaborations in nature—

between sunlight, the atmosphere, the eye, the brain and consciousness itself.

Perhaps that is why the Universe continues to inspire scientists, artists, poets and philosophers alike.

Each seeks to understand the same reality through a different language.

Physics describes it with equations.

Biology explains it through evolution.

Astronomy reveals it across unimaginable distances.

Art captures its beauty.

And the human brain quietly transforms it all into the colourful world we call everyday life.

The Universe is not painted in colours.

It is painted in light.

Our eyes gather that light.

Our brains transform it into colours.

And so, from the moment we are born until the moment we close our eyes for the last time,

we have been walking through a painted dream all along.

"The Universe offers us light.
The human brain offers us colour.

Together they create the beautiful illusion we call seeing."

— Dhinakar Rajaram

Key Takeaways

Science often reveals that reality is far more fascinating than our everyday intuition suggests. The following points summarise the principal ideas explored throughout this article.

Colour does not exist as a physical property of objects.
Objects merely absorb, transmit or reflect different wavelengths of electromagnetic radiation. The sensation of colour arises only after those wavelengths are interpreted by the brain.

Light itself has no colour.
Visible light consists of electromagnetic waves with different wavelengths. Colours are names assigned by the human brain to different portions of the visible spectrum.

The visible spectrum is only a tiny fraction of the electromagnetic spectrum.
Infrared, ultraviolet, radio waves, microwaves, X-rays and gamma rays all exist beyond the limits of human vision.

The retina does not see colour.
Rod cells measure brightness, while cone cells detect different wavelength ranges. Neither understands colour; they merely generate electrical signals.

The brain creates the experience of colour.
Electrical impulses travelling through the optic nerve contain no intrinsic colours. The visual cortex reconstructs colours from patterns of neural activity.

Night vision is naturally almost monochromatic.
Under dim illumination, rod cells dominate our vision, explaining why nebulae, galaxies and landscapes often appear grey despite containing rich colours.

Modern astrophotography reveals colours that are genuinely present.
Long-exposure cameras collect photons over extended periods, allowing faint colours invisible to our eyes to become visible.

Not everyone experiences colour in exactly the same way.
Genetics, age and differences in visual physiology influence colour perception. Some women may even possess tetrachromatic vision, enabling them to distinguish additional colour variations.

Colour vision deficiency is not the absence of sight.
Most individuals with colour vision deficiency see clearly but distinguish certain colours differently because of variations in their cone cells.

The brain constantly edits visual reality.
Optical illusions demonstrate that perception is an active process of interpretation rather than passive recording.

Black-and-white photography highlights the foundations of vision.
Without colour, the brain naturally focuses on contrast, form, texture and illumination, often producing images of remarkable emotional depth.

Very little colour information is often sufficient.
The brain is capable of filling in missing colours from surprisingly small visual cues, illustrating how actively it constructs perception.

Different species experience different visual worlds.
Birds, bees, insects and many other animals perceive wavelengths invisible to humans, reminding us that our perception is only one among countless possible sensory realities.

The Universe exists independently of observers.
Stars, galaxies and photons continue to exist whether or not anyone observes them. Colour, however, exists only as a conscious experience within a suitable nervous system.

Many familiar concepts describe absences rather than physical entities.
Cold is the absence of heat, darkness is the absence of light, silence is the absence of sound, and a shadow is the absence of illumination.

Science does not remove wonder—it deepens it.
Understanding how colour arises transforms an ordinary rainbow into an extraordinary collaboration between sunlight, the atmosphere, the eye, the brain and consciousness.

The Universe provides light.

The eye gathers it.

The brain paints it.

That painting is the colourful world we experience every day.

Glossary of Scientific Terms

Science introduces many specialised terms that may be unfamiliar to some readers. The following glossary explains the important concepts discussed in this article in simple, non-technical language.

After-image

A visual phenomenon in which an image continues to appear after looking away from an object. It occurs because the cone cells in the retina temporarily adapt to prolonged stimulation, causing the brain to perceive complementary colours.

Brain (Visual Cortex)

The region at the back of the brain responsible for processing visual information received from the eyes. It reconstructs shapes, motion, depth and colour from electrical signals arriving through the optic nerve.

Colour

A conscious sensation created by the brain when it interprets different wavelengths of visible light. Colour is not a physical property carried by light or stored inside objects.

Colour Filling-In

A process in which the brain spreads limited colour information across neighbouring regions, creating the impression of a fully coloured object even when only small amounts of colour information are present.

Colour Vision Deficiency (Colour Blindness)

A variation in colour perception caused by missing or altered cone cells. Most affected individuals see normally but have difficulty distinguishing certain colours.

Cone Cells

Specialised light-sensitive cells in the retina that function best in bright light and enable colour vision. Humans normally possess three types of cone cells.

Darkness

The absence or extreme reduction of visible light. Darkness is not a physical substance but simply the condition in which very few photons reach the eye.

Electromagnetic Radiation

Energy that travels through space in the form of waves or particles (photons). It includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.

Electromagnetic Spectrum

The complete range of electromagnetic radiation arranged according to wavelength or frequency. Visible light occupies only a very small part of this spectrum.

Frequency

The number of wave cycles passing a given point each second. Higher frequencies correspond to shorter wavelengths.

Heat

Thermal energy transferred from a warmer object to a cooler one because of a difference in temperature.

Infrared Radiation

Electromagnetic radiation with wavelengths longer than visible red light. Humans cannot see infrared, but many cameras and some animals can detect it.

Optic Nerve

The bundle of nerve fibres that carries electrical signals from the retina to the brain.

Optical Illusion

An image that causes the brain to perceive something differently from the physical reality, revealing how vision depends upon interpretation rather than simple recording.

Photon

The smallest discrete packet (quantum) of electromagnetic radiation. Photons carry energy but possess no colour of their own.

Primary Colours of Light (RGB)

Red, Green and Blue are the three additive primary colours of light. Different combinations of these colours can produce nearly all the colours displayed on digital screens and televisions.

Retina

The light-sensitive layer lining the back of the eye. It contains rods and cones that convert incoming light into electrical impulses.

Rod Cells

Highly sensitive light-detecting cells that function best under dim lighting conditions. Rods detect brightness but cannot distinguish colours.

Shadow

A region where light is blocked by an opaque object. A shadow is not an object but the absence of illumination.

Silence

The absence of significant sound waves reaching the ears. Silence is not a physical substance but simply the lack of detectable sound.

Tetrachromacy

A rare form of colour vision, found mainly in some women, involving four functionally distinct types of cone cells. Tetrachromats may distinguish subtle colour differences invisible to most people.

Thermal Energy

The energy associated with the random motion of atoms and molecules. Higher thermal energy corresponds to higher temperatures.

Trichromacy

Normal human colour vision based on three different classes of cone cells sensitive to short, medium and long wavelengths.

Ultraviolet Radiation

Electromagnetic radiation with wavelengths shorter than visible violet light. Although invisible to humans, many insects and birds can detect ultraviolet light.

Vacuum

A region containing extremely little matter. Even the emptiest parts of space are not perfectly empty.

Visible Spectrum

The narrow range of electromagnetic wavelengths detectable by the human eye, extending approximately from 380 to 700 nanometres.

Wavelength

The distance between two successive peaks of a wave. Different wavelengths of visible light are interpreted by the brain as different colours.

Understanding these terms transforms familiar everyday experiences into a deeper appreciation of the remarkable science underlying human vision.

Frequently Asked Questions (FAQ)

The science of colour often raises fascinating questions because it challenges many of our everyday assumptions. Here are answers to some of the most commonly asked questions related to colour perception, vision and the physics of light.

1. Does colour actually exist?

Not as an independent physical property. The external world contains electromagnetic radiation of different wavelengths. The sensation we call colour is created by the brain after interpreting those wavelengths.

2. Is light itself coloured?

No. Light consists of electromagnetic waves (or photons) of different wavelengths. Colour is the brain's interpretation of those wavelengths, not a property carried by the light itself.

3. Why does a red apple appear red?

A red apple absorbs most wavelengths of visible light and reflects wavelengths corresponding to red. Your cone cells detect the reflected light, and your brain interprets those signals as the colour red.

4. Why is the sky blue?

The Earth's atmosphere scatters shorter wavelengths of sunlight more efficiently than longer wavelengths. This process, known as Rayleigh scattering, causes the sky to appear blue during the day.

5. Why are sunsets often red or orange?

At sunrise and sunset, sunlight travels through a much thicker layer of the atmosphere. Most blue light is scattered away, allowing longer red and orange wavelengths to dominate the light reaching our eyes.

6. Why do stars and nebulae often appear grey through a telescope?

Most deep-sky objects are extremely faint. Under such low light levels, the rod cells in our eyes dominate vision. Rods detect brightness but cannot distinguish colours, causing nebulae and galaxies to appear grey or nearly colourless.

7. Why do astrophotographs show brilliant colours?

Modern cameras can collect light for many seconds, minutes or even hours. By accumulating millions of photons, they record faint colours that are invisible to the human eye during direct observation.

8. Can two people see the same colour differently?

Yes. Small genetic differences, ageing, lighting conditions and individual variations in cone cells mean that colour perception differs slightly from person to person.

9. Do women generally see more colours than men?

On average, women tend to distinguish subtle colour differences slightly better than men. Some women may possess tetrachromatic vision, giving them four functioning cone types instead of the usual three, allowing them to perceive additional colour variations.

10. What is tetrachromacy?

Tetrachromacy is a rare form of colour vision in which an individual possesses four functionally distinct cone types. This may enable the perception of colour differences invisible to most people.

11. What is colour blindness?

More accurately called colour vision deficiency, it occurs when one or more types of cone cells are absent or function differently. It affects colour discrimination rather than overall eyesight.

12. Why can we see better at night but not in colour?

Rod cells are far more sensitive to dim light than cone cells. At night, rods dominate vision, enabling us to see faint objects but largely without colour.

13. Do animals see colours differently?

Yes. Bees can detect ultraviolet light, many birds have four cone types, mantis shrimps possess even more complex visual systems, while many mammals perceive fewer colours than humans.

14. Why do optical illusions fool us?

The brain constantly interprets incomplete visual information using experience and probability. Optical illusions exploit these shortcuts, revealing that perception is an active process rather than a perfect recording of reality.

15. Can a black-and-white image appear coloured?

Yes. With carefully placed coloured lines or dots, the brain can spread colour information across neighbouring regions, creating the impression of a fully coloured image even though most of it remains monochrome.

16. Why do old black-and-white photographs feel so expressive?

Without colour, the brain focuses more strongly on contrast, lighting, texture, composition and emotion. Many photographers deliberately use monochrome to emphasise these qualities.

17. Does darkness exist?

Darkness is not a physical substance. It is simply the absence or significant reduction of visible light reaching our eyes.

18. Does cold exist?

In physics, cold is not an independent entity. It describes a condition of lower thermal energy. What we experience as cold is the result of heat leaving our bodies.

19. If no one were looking at the Universe, would colours still exist?

The Universe would still contain light, wavelengths and electromagnetic radiation. However, the conscious experience of colour would not exist without a suitable visual system to interpret that light.

20. What is the most important message of this article?

The physical Universe consists of light, matter and the laws of physics. Colour is one of the brain's greatest achievements—a vivid interpretation of electromagnetic radiation that allows us to understand and appreciate the world around us.

Science often begins by questioning the obvious.

Colour is one of its most beautiful answers.

References & Further Reading

The concepts discussed in this article draw upon well-established principles of physics, optics, neuroscience, astronomy and visual perception. Readers wishing to explore these subjects in greater depth may find the following references useful.

Books

Bruce Benamran.
Why Does E = mc²? (and Why Should We Care?)
John Murray, London.

Richard P. Feynman, Robert B. Leighton & Matthew Sands.
The Feynman Lectures on Physics, Volume I.
Addison-Wesley.

David J. Griffiths.
Introduction to Electrodynamics (4th Edition).
Pearson Education.

Eugene Hecht.
Optics (5th Edition).
Pearson.

Brian Wandell.
Foundations of Vision.
Sinauer Associates.

Margaret Livingstone.
Vision and Art: The Biology of Seeing.
Harry N. Abrams.

Oliver Sacks.
An Anthropologist on Mars.
Vintage Books.

Carl Sagan.
Cosmos.
Ballantine Books.

Neil deGrasse Tyson & Donald Goldsmith.
Origins: Fourteen Billion Years of Cosmic Evolution.
W.W. Norton & Company.

Sidney Perkowitz.
Empire of Light: A History of Discovery in Science and Art.
Joseph Henry Press.

Selected Scientific Papers

Young, T. (1802). On the Theory of Light and Colours.
Helmholtz, H. von. Treatise on Physiological Optics.
Edwin H. Land. The Retinex Theory of Colour Vision.
Hubel, D. H. & Wiesel, T. N. Research on visual processing in the cerebral cortex.
Studies on tetrachromacy and human colour perception published in peer-reviewed journals including Nature, Science and the Journal of Vision.

Astronomy & Space Agencies

NASA – Hubble Space Telescope
NASA – James Webb Space Telescope
European Space Agency (ESA)
ESA/Hubble Image Archive
European Southern Observatory (ESO)

Educational Organisations

The Royal Institution
The Royal Society
The Optical Society (Optica)
American Physical Society (APS)
Institute of Physics (IOP)
The International Commission on Illumination (CIE)

Topics Worth Exploring Further

The Electromagnetic Spectrum
Rayleigh Scattering
Mie Scattering
Human Eye Anatomy
Rod and Cone Cells
Colour Constancy
Opponent Process Theory
Colour Blindness and Colour Vision Deficiency
Tetrachromacy
Optical Illusions
Visual Neuroscience
Digital Colour Spaces (RGB, CMYK, HSV)
CCD and CMOS Image Sensors
Astrophotography
False-colour Astronomy Images
Infrared Astronomy
Ultraviolet Astronomy
James Webb Space Telescope Imaging
Human Perception and Consciousness

Author's Note

This article has been written as an educational science communication piece intended for students, teachers, amateur astronomers, photographers, artists and all readers who enjoy understanding the deeper science behind everyday experiences.

Although every effort has been made to ensure scientific accuracy, complex topics have occasionally been simplified to improve accessibility for a general audience. Readers are encouraged to consult the references listed above for more advanced and detailed treatments of optics, neuroscience and visual perception.

The pursuit of knowledge begins with curiosity.

Science transforms that curiosity into understanding.

Copyright, Educational Use & Intellectual Property Notice

This article has been researched, conceptualised, written and presented by Dhinakar Rajaram as an original work of science communication intended to make complex scientific ideas accessible to students, educators, amateur astronomers, science enthusiasts and the general public.

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Unless otherwise acknowledged, the following elements of this publication constitute original intellectual property and are protected under applicable copyright laws:

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Personal recollections and experimental experiences described within the article, including the author's childhood RGB television experiment.
Original scientific discussions that synthesise concepts from multiple disciplines including physics, astronomy, optics, neuroscience and biology.
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Scientific facts, laws, mathematical principles and established theories discussed in this article belong to humanity's shared body of scientific knowledge and are naturally not subject to copyright.

However, the author's original selection, organisation, explanation, presentation, illustrations, examples, educational interpretation and literary expression of those scientific concepts are protected intellectual property.

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Where practical, attribution should include the author's name together with a link to the original publication.

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Artificial intelligence tools were used solely as editorial assistants to improve language, formatting and presentation.

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Accuracy Notice

Every reasonable effort has been made to ensure scientific accuracy based upon the current understanding of physics, optics, neuroscience, astronomy and visual perception at the time of publication.

Science continually evolves through new discoveries. Readers are encouraged to consult current scientific literature for the latest developments in these fields.

Acknowledgement

The author gratefully acknowledges the countless scientists, astronomers, physicists, biologists, neuroscientists, educators and science communicators whose discoveries over many generations have expanded humanity's understanding of the natural world.

This article seeks to honour their contributions by presenting established scientific knowledge in a form that is accessible, engaging and inspiring to readers of all backgrounds.

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Readers are warmly encouraged to share the original link to this article through social media, educational groups, astronomy clubs, science forums and personal networks.

Sharing the original publication ensures that readers receive the most accurate, complete and up-to-date version while properly acknowledging the author's work.

Knowledge grows when it is shared responsibly.

Curiosity inspires discovery.

Understanding enriches humanity.

Thank you for reading.

Acknowledgements

Science is a collective human endeavour spanning thousands of years. Every scientific article written today stands upon the observations, experiments and discoveries of countless men and women who devoted their lives to understanding nature.

Although this article is an original work of science communication, the scientific principles discussed herein are founded upon the pioneering contributions of physicists, astronomers, mathematicians, neuroscientists, biologists, physiologists, photographers and educators from many generations.

The author expresses sincere gratitude to these remarkable individuals whose curiosity has continually expanded humanity's understanding of the Universe.

To the Scientific Community

Special appreciation is extended to the worldwide scientific community whose rigorous research has shaped our present understanding of optics, light, colour vision, neuroscience, astronomy and the electromagnetic spectrum.

Every experiment conducted, every paper published and every observation carefully recorded contributes another small piece to humanity's ever-growing understanding of nature.

To Science Communicators and Educators

The author gratefully acknowledges the countless teachers, professors, lecturers, science communicators, museum educators, documentary filmmakers and popular science writers who continue to make complex scientific ideas understandable and inspiring for the general public.

Their dedication demonstrates that scientific knowledge becomes most valuable when it is shared openly, clearly and responsibly.

A Personal Reflection

Curiosity often begins long before we realise it.

One of the memories described in this article recalls a childhood attempt to create colour by placing red, green and blue transparent sheets over the screen of a black-and-white television.

At the time, it was simply a playful experiment carried out by an inquisitive six-year-old.

Looking back after more than four decades, it seems that this small act of curiosity quietly planted the seeds for a lifelong fascination with science, astronomy, physics and the hidden mechanisms through which nature reveals itself.

This article is, in many ways, a continuation of that same curiosity.

To the Reader

Finally, my heartfelt thanks go to every reader who has chosen to spend time exploring this article.

Whether you are a student, teacher, amateur astronomer, photographer, artist, engineer, scientist or simply someone who enjoys asking questions about the world, your curiosity helps keep science alive.

Knowledge grows through questions. Understanding grows through exploration. Wonder grows through discovery.

If this article encourages even one reader to look a little more closely at a rainbow, a sunset, a flower, the night sky or even an ordinary black-and-white photograph, then it has fulfilled its purpose.

Science begins with observation.

Observation awakens curiosity.

Curiosity leads to understanding.

Understanding reveals the extraordinary hidden within the ordinary.

— Dhinakar Rajaram

About the Author

Dhinakar Rajaram is an independent science writer, amateur astronomer, railway enthusiast and lifelong student of the natural world. Driven by an enduring curiosity about how everyday phenomena arise, he enjoys exploring the fascinating connections between physics, astronomy, engineering, mathematics, biology and the history of science.

Rather than viewing science as a collection of complex formulae, he believes it is a way of understanding the ordinary world with extraordinary clarity. Many of his articles originate from simple observations—a cup of tea, a passing train, a spider's web, a sunset, the night sky, or an everyday object—which are then explored through established scientific principles and presented in an engaging and accessible manner.

His science writing seeks to bridge the gap between scientific accuracy and public understanding, making complex topics approachable for readers of all ages without sacrificing scientific rigour. Each article combines careful research with original explanations, thoughtfully designed illustrations, historical context and, where appropriate, personal observations or experiments that inspire further curiosity.

Astronomy occupies a special place among his interests. Whether observing the Moon through a telescope, following planetary movements, studying comets, exploring deep-sky objects or examining the science behind historical astronomical events, he believes that the night sky remains one of humanity's greatest classrooms.

His interests also extend to railway engineering, fluid dynamics, optics, meteorology, photography, mathematics, geology, acoustics and the many hidden scientific principles that quietly shape our everyday lives. Through interdisciplinary exploration, he enjoys revealing how seemingly unrelated subjects often connect in unexpected and beautiful ways.

Above all, he believes that science belongs to everyone—not only to laboratories and universities, but also to curious minds willing to observe, ask questions and seek evidence. Every ordinary observation has the potential to become the beginning of an extraordinary scientific journey.

Philosophy

"The greatest discoveries often begin with the simplest questions.

Observe carefully.
Question fearlessly.
Think critically.
Remain curious.

Nature is always willing to teach those who are willing to notice."

Areas of Interest

Astronomy & Observational Astronomy
Physics & Everyday Science
Optics & Human Vision
Railway Engineering & Operations
Fluid Dynamics
Meteorology & Atmospheric Science
Mathematics in Nature
History of Science
Photography & Scientific Imaging
Scientific Illustration & Public Science Communication

"Science is not merely about finding answers.

It is about learning to ask better questions."

— Dhinakar Rajaram

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Monday, 29 June 2026