Young–Helmholtz theory

Young–Helmholtz theory proposes that color vision begins with three receptor types, each most sensitive to a different range of wavelengths. Their combined responses help the visual system distinguish colors.

Trichromacy: Color vision based on three independent channels of sensitivity. The theory is a foundational account of trichromatic color vision.
Thomas Young: An English physician and polymath whose work ranged across physics, physiology, and linguistics. Young proposed that the eye uses a limited number of receptor types to encode color.
Opponent-process theory: A theory that explains color vision through opposing neural channels such as red–green and blue–yellow. It describes later color processing that a simple three-receptor account does not capture.
CIE 1931 color space: A standardized mathematical representation of visible colors based on human color-matching data. Its color-matching foundations reflect the three-variable structure associated with trichromacy.
Cone cell: A retinal photoreceptor that supports daylight vision and color discrimination. The theory’s three receptor types correspond broadly to cone classes in the retina.
Hermann von Helmholtz: A German physician and physicist who made major contributions to physiology and optics. Helmholtz developed and defended Young’s account using physiological and psychophysical evidence.
Color constancy: The tendency for perceived surface colors to remain stable across changes in illumination. Receptor responses alone do not explain how perception compensates for changing light.
RGB color model: A color model that represents colors as combinations of red, green, and blue components. RGB systems exploit three primary signals to reproduce many colors for trichromatic observers.
Photopsin: A light-sensitive protein in cone cells that helps determine their wavelength sensitivity. Different cone photopsins provide the unequal spectral sensitivities underlying the model.
Color vision: The visual capacity to distinguish light by its spectral composition and resulting appearance. The theory is one influential explanation of how color vision works.

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Color matching (trichromacy)Related: The physiological framework the matching results were read against.