Colour is not just something we look at; it is part of how the world shows up for us. It shapes mood and memory, hints at time of day and change of season, signals danger and safety, belonging and difference. A grey sea under a low sky can feel heavier than the same water caught blue by noon light. A saffron cloth can mark the sacred or the celebratory long before any words do. To ask what colour is—and why it matters—is to ask how mind, body, and world are braided together.
This essay is a tour through that braid. We’ll move from physics to physiology, from art to everyday life, and from classic philosophy to contemporary science. Along the way, we’ll see why colour is both stubbornly objective (bound to the optics of light and surfaces) and irreducibly subjective (bound to a living eye and a perceiving body). We’ll also see how artists and designers have long acted as field scientists of perception, experimenting with colours to reveal how seeing really works.
1) What exactly is “colour”?
If you ask a physicist, colour begins with light—electromagnetic radiation distributed across wavelengths. Shorter visible wavelengths we call “blue/violet,” longer ones “red.” Sunlight disperses through a prism into a spectrum, as Isaac Newton famously demonstrated in Opticks (1704), arguing that white light is a mixture of differently “refrangible” rays and that prismatic refraction separates those constituents rather than painting them in transit. He also stressed a crucial point that will echo throughout this essay: colour, as we experience it, is a sensation produced in the mind. (Project Gutenberg, newtonproject.ox.ac.uk, Wikipedia)
Why is the sky blue? Not because the air is painted that way, but because small particles in the atmosphere scatter shorter wavelengths more effectively than longer ones—a process called Rayleigh scattering. That physical fact, paired with our visual system’s tuning, yields the familiar dome of blue by day and the reddening of sunsets when the sun’s light passes through more atmosphere. (ScienceDirect)
So far, so physical. But colours as we see them are not just wavelengths. Two lights with very different spectral makeups can look the same—an effect called metamerism. Metamers remind us that colour experience depends on how a visual system samples and calculates from the incoming energy, not just on the energy “out there.” (Encyclopedia Britannica)
2) How the eye and brain build colour
Humans are typically trichromats: we have three classes of cone photoreceptors in the retina, each containing a pigment with a different spectral sensitivity (often labelled S, M, and L for short-, medium-, and long-wavelength peaks). In the 19th century, Thomas Young and Hermann von Helmholtz proposed that mixture signals from three cone types underlie our hue experiences—the trichromatic theory—now a cornerstone of colour science. (Britannica Kids)
Ewald Hering, noticing facts trichromacy couldn’t neatly explain (like “reddish-green” being ill-formed while “yellowish-green” is fine), proposed the opponent-process theory. On this view, the visual system recombines cone signals into opponent channels: red vs. green, blue vs. yellow, and a luminance channel (light vs. dark). Modern neuroscience shows both ideas are true at different stages: cones mix linearly, and later neural circuitry computes opponent signals. (Encyclopedia Britannica)
In primary visual cortex (V1) and beyond, researchers have identified neurons that respond to spatial chromatic contrast, including so-called double-opponent cells thought to contribute to colour-edge detection and colour constancy (your ability to recognize a ripe banana as “yellow” whether you’re indoors at dusk or outside at noon). Evidence from physiology and modelling supports these mechanisms, though debates continue about the exact division of labour across visual areas. (PMC, jneurosci.org, ScienceDirect)
A complementary line of work, starting with Edwin Land’s Retinex theory, showed that the brain uses scene-wide comparisons to stabilize colour appearance under changing illumination. Land’s experiments with “Mondrian” patches revealed that perceived colour depends on ratios across the whole field, not on a pixel’s absolute wavelength composition. Modern formulations continue to inform both neuroscience and computer vision. (cnbc.cmu.edu, PNAS, McCann Imaging)
Want a vivid demonstration of how context rules colour? Look up Edward Adelson’s Checker Shadow illusion: two squares with identical pixel values look strikingly different because the brain discounts the (implied) shadow and interprets local contrasts. Your eyes are not broken; they are doing clever inference. (persci.mit.edu)
For a readable overview of the neural story—from cones to cortex—see reviews by Gegenfurtner & Kiper and by Conway and colleagues. (annualreviews.org, ResearchGate)
3) Philosophers on colour: object, mind, or relation?
Philosophers have long wrestled with how colours fit into a scientific picture of the world. Early modern thinkers like Galileo and Locke framed colours as secondary qualities—not intrinsic to objects in the way shape or size might be, but dispositions of objects to produce certain experiences in us. The contemporary debate, surveyed in the Stanford Encyclopedia of Philosophy, swings among eliminativism (“strictly speaking, nothing is really coloured”), subjectivism (“colours are properties of experience”), and realism or relationalism (colours as objective-but-relational properties involving observer and conditions). (Stanford Encyclopedia of Philosophy)
Ludwig Wittgenstein’s late notes, published as Remarks on Colour, didn’t offer a theory so much as a map of our colour concepts—why some combinations are possible (bluish-green) and others absurd (greenish-red)—nudging us to see that grammar, usage, and perception intertwine. (Dokumen)
Maurice Merleau-Ponty, in a different key, emphasized that perception is not a series of inner “pictures” but a bodily comportment in a world already meaningful: colour belongs to things as they appear within a lived field—“the visible and the invisible” are folded together rather than split between object and subject. That phenomenological stance complements science by reminding us that how colour shows up in human life is not captured by wavelengths alone. (Stanford Encyclopedia of Philosophy)
One famous puzzle, Frank Jackson’s “Mary’s room” thought experiment, asks whether a brilliant scientist who knows all the physical facts about colour but has never seen it learns something new on seeing red for the first time. Many take this “knowledge argument” to show there’s an irreducibly phenomenal aspect to colour experience; others reply that Mary gains a new ability or perspective, not new propositional facts. Either way, the argument forces us to square third-person explanations with first-person life. (Simon Fraser University, Stanford Encyclopedia of Philosophy)
4) Language, culture, and the names of colours
Do we all “carve up” the colour spectrum the same way? The classic 1969 study Basic Color Terms by Brent Berlin and Paul Kay argued that languages introduce colour terms in a partially predictable order (black/white → red → green/yellow → blue → brown → purple/pink/orange/grey) and that certain “focal” hues feel universally salient. Subsequent work has refined and critiqued aspects of their thesis, but their core insight—that biology and culture both shape colour naming—remains central. (Internet Archive)
Anthropology and psycholinguistics continue to show a dance between shared human hardware (cones, opponent channels, constancy mechanisms) and local cultural practice (which shades get words, which colours become symbolically loaded). Our categories are neither arbitrary nor fully dictated by nature.
5) Artists as field scientists of colour
The studio has long been a lab for vision. Wassily Kandinsky treated colour as a carrier of inner resonance—arguing in Concerning the Spiritual in Art that certain hues and contrasts evoke distinct “vibrations of the soul.” Whether or not one buys the metaphysics, Kandinsky’s practice made a crucial empirical point: colour’s meaning depends on form, adjacency, and context. (Project Gutenberg)
At the Bauhaus, Johannes Itten systematized exercises on hue, value, and saturation, proposing seven “contrasts of colour” (including contrast of hue, light–dark, warm–cool, complementary, saturation, simultaneous contrast, and extension). Students learned firsthand that the same pigment can look different depending on its neighbours—an artistic encounter with metamerism’s phenomenological cousin. (papers.cumincad.org)
Mid-century, Josef Albers’s Interaction of Color became a playbook for designers to see interactions rather than think them. He urged learners to treat colours as “deceivers,” training the eye through experiments where a single paper swatch could appear as two different hues against different grounds. His approach presaged today’s emphasis on perceptual testing over armchair theory. (Internet Archive)
These artistic traditions converge with science: the way a yellow-green leaf shifts under warm sunset light is not just poetic; it’s a live demonstration of the brain’s constancy computations. Land’s Mondrians could easily hang next to Albers’s studies. (McCann Imaging)
6) Why colour enriches experience (and sometimes changes behaviour)
Colour does more than decorate; it guides attention, communicates affordances, and can influence feelings and choices—though context is everything. A large review by Andrew Elliot and Markus Maier synthesizes evidence that, for example, red can prime avoidance in achievement contexts (think “red ink” or “marked wrong”), while also signalling attraction in interpersonal contexts. Effects are typically small-to-moderate and depend on task and culture, but the overall picture is clear: colour is psychologically active. (Datacolor)
None of this means colours have fixed, universal meanings. It does mean designers and artists should treat colour as information with potential effects—subject to testing rather than folklore. And it means the everyday saturation of our environments (from safety signage to UI buttons) is part of how we learn to see with colour, not just see colour.
7) When colour is different: variability and colour vision deficiency
Not everyone samples the spectrum with the same hardware. Inherited red–green colour-vision deficiency (CVD), usually X-linked, affects a nontrivial share of the population: around 8% of men and ~0.4–1% of women worldwide depending on ancestry and sample, with deutan (M-cone related) more common than protan (L-cone) forms. This isn’t a minor footnote—it’s part of the world’s visual diversity. (PubMed, PMC, Nature)
Design and philosophy meet here. If colour is one thread in how reality is disclosed to us, then different cone sets disclose the world differently. That is not a deficit in a moral sense; it’s a difference in available distinctions. For wayfinding, safety, or data visualization, it’s good practice to couple colour with shape, value, or texture so information survives across observers. (Artists have long done this instinctively: compare how value structure carries form even in monochrome.)
8) Colour constancy, illusions, and why perception is not a camera
It’s tempting to think “seeing is measuring.” In fact, seeing is inferring—rapidly, mostly correctly, sometimes spectacularly wrong. The same surface reflects different spectral mixtures under different lights; your brain seeks the stable property (reflectance) by discounting changes in illumination. The flip side of that gift is vulnerability to illusions—like Adelson’s checker-shadow—where cues trigger the constancy machinery and your experience departs from the raw numbers on a display. (persci.mit.edu, Wikipedia)
Philosophically, illusions are not bugs but data: they show the rules your brain uses to construct a coherent world. Scientifically, they motivate models from double-opponent coding in V1 to higher-level contextual computations described by Retinex-like algorithms. (PMC, McCann Imaging)
9) Reconciling physics and phenomenology
Back to the opening tension: is colour “out there” or “in here”? Newton’s prism says wavelengths and refractive indices matter; Wittgenstein and Merleau-Ponty say grammar and embodiment matter. Neuroscience says cone responses and opponent channels matter; anthropology says language and culture matter. The most sensible view takes these as layers of one phenomenon.
The philosopher’s catalogue of positions helps:
- Eliminativists/subjectivists emphasize that science doesn’t find “redness” in the world, only reflectance curves and neuronal firings.
- Realists/relationalists say colours are real but relational—properties that objects have relative to standard conditions and typical observers.
- Dispositionalists treat colours as capacities to produce certain experiences.
The Stanford Encyclopedia of Philosophy surveys these disputes and shows why no single reduction wins easily. Colours behave too lawfully to be dismissed as private fictions, and too observer-dependent to be simple intrinsic properties of matter. (Stanford Encyclopedia of Philosophy)
A helpful everyday translation: colours are world-bound patterns that only come to life in seeing systems like ours. That is, they are neither mere hallucination nor mere radiation; they are how a lived body registers a lit world.
10) Practicing colour: habits of attention
You don’t need a lab or a studio to study colour. Try these field exercises:
- Chase constancy. Take a single object (a shirt, a fruit) and photograph it under morning sun, shade, fluorescent office light, and sunset. Notice how your experience stays “the same colour” while the camera reports strikingly different RGBs. That gap is your brain’s computation at work—a little Retinex in your pocket. (Scientific American)
- Neighbor effects. Place one coloured paper on two different backgrounds (say, warm grey vs. cool grey). Watch it “shift.” That’s Albers’s lesson: never judge a colour alone. (Internet Archive)
- Language audit. Keep a one-day log of colour words you hear or say. Which terms come easily? Which require pointing rather than naming? You’ll be re-enacting Berlin & Kay’s observation that naming is systematic yet limited—some experiences outrun our lexicon. (Internet Archive)
- Accessibility check. Take a graphic or chart you’ve made and test it with a red-green CVD simulator or, simpler, print it in greyscale. If the message survives, your design respects visual diversity. (CVD prevalence data make the case without drama.) (PubMed)
11) Colour, meaning, and care
Because colours carry affective weight, they can help or hinder. Reviews in colour psychology caution that effects are context-sensitive (the same red that signals error in an academic test might signal appetite on a restaurant sign). The practical upshot is not superstition (“always use blue for trust”) but hypothesis and test—treat colour choices as experiments with human attention and feeling. (Datacolor)
The ethical upshot is attentiveness: colour is part of how spaces include or exclude. High-chroma, high-contrast environments may energize some and overwhelm others; low-contrast signage may be beautiful and useless. If perception is an achievement of body and world together, we owe each other worlds that are easier—more legible—to achieve.
12) A short timeline of the idea of colour
- Plato & Aristotle offered early taxonomies of colours and elements, anchoring later debates that confused “light” with “whiteness.”
- Newton empirically broke white light into a spectrum and argued for mind-dependent colour experiences tied to physical optics. (Project Gutenberg)
- Young–Helmholtz gave us trichromacy; Hering gave us opponents; physiology and psychophysics later braided them into a stage-wise account. (Britannica Kids, Encyclopedia Britannica)
- Goethe resisted Newton’s physics-first approach, focusing on lived phenomena and complementary pairs—hugely influential in art and pedagogy even if unpersuasive to physics. (Project Gutenberg)
- Itten and Albers trained generations to see interactions; Kandinsky pursued colour’s inner resonance. (papers.cumincad.org, Internet Archive, Project Gutenberg)
- 20th–21st c. neuroscience linked cortical coding, double-opponent cells, and constancy; Retinex framed global comparisons; current work refines these stories. (PMC, McCann Imaging)
- Philosophy today navigates between eliminativism and relational realism, under an umbrella that recognizes both hard science and lived meaning. (Stanford Encyclopedia of Philosophy)
13) Why colour matters—for life, not just for pictures
Colour is not icing on perception; it’s part of the cake. It lets us read ripeness and rust, track time and weather, parse scenes at a glance. It animates rituals, brands, and identities; it orchestrates interiors and skies alike. In Merleau-Ponty’s spirit, it is one way the world and the body meet—not two things, but one relation.
That relation is robust enough to survive shadows and changes in light; flexible enough to function with different cones; subtle enough to be bent by adjacency and naming; powerful enough to nudge choice and feeling. The wonder is not that we sometimes mis-see; it is that we so often see through noise to the stable properties that matter for life.
So the next time a hillside looks “more green” after rain, or a saffron flag glows at dusk, know that physics, physiology, culture, and care are all at work. You are not merely looking at colour; you are participating in a world that becomes legible—becomes lovable—through it.
Sources & further reading (selected)
- Newton, Opticks (1704), Project Gutenberg / Newton Project. (Project Gutenberg, newtonproject.ox.ac.uk)
- Britannica, “Why the sky is blue” (Rayleigh scattering). (ScienceDirect)
- Wyszecki & Stiles–style overview of metamerism (see encyclopedic treatment). (Encyclopedia Britannica)
- Young–Helmholtz trichromatic theory; Hering opponent theory (Britannica overviews). (Britannica Kids, Encyclopedia Britannica)
- Double-opponent coding and colour in cortex (Shapley review; Johnson et al.). (PMC, jneurosci.org)
- Land’s Retinex theory and follow-ups (Scientific American; PNAS). (cnbc.cmu.edu, PNAS, McCann Imaging)
- Adelson’s Checker Shadow illusion (MIT). (persci.mit.edu)
- Elliot & Maier, “Color and psychological functioning” (review). (Datacolor)
- Berlin & Kay, Basic Color Terms (1969). (Internet Archive)
- Stanford Encyclopedia of Philosophy entries on Color and on the Knowledge Argument. (Stanford Encyclopedia of Philosophy)
- Frank Jackson, “Epiphenomenal Qualia” (1982). (Simon Fraser University)
- Wittgenstein, Remarks on Colour. (Dokumen)
- Merleau-Ponty overviews (SEP). (Stanford Encyclopedia of Philosophy)
- Kandinsky, Concerning the Spiritual in Art. (Project Gutenberg)
- Itten’s “seven contrasts”; Albers, Interaction of Color. (papers.cumincad.org, Internet Archive)
- Prevalence of red–green CVD (Birch; Simunovic; reviews). (PubMed, Nature)
Accessible neuroscience reviews (Gegenfurtner & Kiper; Conway et al.). (annualreviews.org, ResearchGate)
