Color matching (trichromacy)

The experimental fact that any light can be matched by mixing three primaries, the foundation of trichromatic color vision and quantitative colorimetry.

Trichromatic theory: The theory that color vision rests on three receptor types, so any stimulus is encoded by three numbers. Three primaries suffice because the retina itself reduces light to three signals.
Maxwell's color matching experiments: James Clerk Maxwell's 1850s disk and prism experiments first quantifying three-primary color matching. The original color-matching measurements, producing the first triangular chromaticity diagram.
Thomas Young: Physician and physicist who proposed in 1802 that the retina contains three kinds of color receptors. His three-receptor hypothesis explained why three primaries suffice.
Newton's color spectrum: Newton's demonstration that white light is a mixture of spectral components refracted by a prism. Made light composition measurable, the precondition for mixing experiments.
Opponent process theory: Ewald Hering's theory that color is coded by red–green, blue–yellow, and light–dark opponent channels. Explains hue cancellation that trichromatic matching alone cannot; both stages are real.
Cone cells: Retinal photoreceptors of three types, each with a distinct spectral sensitivity, that transduce light into neural signals. The three cone types are the physical reason a three-variable match is always possible.
Wright–Guild color matching data: The 1920s observer experiments by W. D. Wright and John Guild that the CIE averaged into its 1931 standard. The empirical dataset underlying the CIE 1931 color-matching functions.
James Clerk Maxwell: Physicist who performed the first quantitative trichromatic matching experiments and invented color photography. Turned trichromacy from theory into measured color-matching functions.
Grassmann's laws: Hermann Grassmann's 1853 proof that color matching obeys linear vector-space rules. The mathematical insight that made matching data transformable between primaries.
Color appearance models: Models such as CIELAB and CIECAM that predict perceived color under changing viewing conditions. Matching functions predict equality of stimuli, not how colors appear under adaptation.

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