How do the colors work?

Light enters the eye, and cone cells compare wavelengths

The physical side of color starts with light. Newton's prism experiments showed that white light can be separated into a spectrum, which established that color is connected to the physical composition of light rather than being added by the prism itself [4]. In the eye, physiology turns that light into signals: the retina contains cone cells that respond differently to different wavelengths, and their combined activity is the first step toward color [2].

A key part of this early stage is cone-opponent processing. Rather than sending separate channels for red, green, and blue, the retina compares cone signals against each other, so one pathway is excited by some wavelengths and inhibited by others [1]. This comparison is the biological basis for why some colors seem to oppose each other, such as reddish versus greenish.

The old opponent-pairs story is incomplete, not the whole answer

For 150 years, Hering's Opponent-Colors Theory dominated explanations of color appearance. It claimed two things: that any color can be described by how reddish-versus-greenish, bluish-versus-yellowish, and blackish-versus-whitish it looks, and that each of these pairs is hard-wired into a separate brain mechanism [1]. A 2023 review concludes that neither claim holds up: the theory is wrong as stated [1].

The replacement proposal, called Utility-Based Coding, keeps the retinal cone-opponent mechanisms but changes their role. On this view, those mechanisms are an efficient way to encode spectral information while also preserving high-acuity spatial detail, and the color categories we experience are an adaptive output of the brain shaped by behavioral demands rather than fixed innate pairs [1]. This is a proposed model, not a settled replacement, but it reframes color as something the brain constructs for use rather than reads off a fixed wiring diagram.

In the brain, color becomes a stable hue through network interactions

Single neurons in the early visual pathway respond to chromatic stimuli, but how those cells interact to produce a stable perception of hue is still not fully known [5]. A dynamical model of the primary visual cortex proposes that hue selectivity emerges from interactions within the cortical network, and that a thresholding nonlinearity helps sharpen tuning so chromatic stimuli can be encoded precisely [5].

The same model also offers an explanation for color experiences without a stimulus: in the absence of input, the network can produce hallucinatory color perception through a Turing-like mechanism of biological pattern formation [5]. That is a model-based possibility, not a direct observation, but it illustrates how much of color experience may come from the brain's own dynamics rather than from the light alone.

Mixing light and mixing paint follow different rules

One practical consequence of how color works is that additive and subtractive mixing are not the same. Additive color theory describes how colors are created by combining light, and it is the basis for color in digital displays and light-based art [3]. Subtractive color theory, which involves paints and pigments, works by removing wavelengths from light rather than adding them [3].

This distinction matters for learning and for art: additive color is often overshadowed by subtractive color in school art curricula, even though light-based color is central to screens and digital media [3]. Devices designed to demonstrate additive mixing with light aim to make that difference visible for learners [3].

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