Color constancy

The visual system's ability to perceive an object's surface color as stable even when the light illuminating it changes dramatically.

Chromatic adaptation: The visual system's adjustment of its sensitivity to offset the color bias of the prevailing illumination. The first and best understood mechanism: receptors recalibrate so a warm-lit scene looks neutral.
Land's color-mondrian experiment: Land's 1970s demonstration that patches keep their apparent color when lit by three adjustable light sources. The canonical laboratory display that launched modern quantitative work on constancy.
Trichromatic theory: The theory that color is signaled by three cone types with different spectral sensitivities. The three-dimensional cone responses are the raw, illumination-contaminated input constancy must correct.
Color realism: The philosophical view that colors are real properties of object surfaces, not mind-dependent experiences. Constancy is realism's best psychological evidence that color belongs to objects, not lights.
Edwin Land: Polaroid inventor who proposed Retinex theory and staged influential constancy demonstrations. His two-color projections and mondrian experiments reframed constancy as a computation.
Retinex theory: Edwin Land's proposal that the brain computes surface lightness independently across three wavelength bands. An explicit computational account of how comparisons across regions recover surface color.
Checker shadow illusion: Adelson's demonstration that two identical gray squares appear different under inferred shadow and light. Shows the lightness version of constancy, where the illuminant is inferred rather than known.
Spectral reflectance: The fraction of light a surface reflects at each wavelength, the physical basis of object color. Constancy is the recovery of this stable surface property from changing retinal signals.
Sensationism: The view that color experience is fully determined by momentary retinal stimulation. Constancy refutes this: identical retinal input under different scenes yields different color judgments.
Ewald Hering: Nineteenth-century physiologist who proposed opponent color coding and the concept of memory color. His opponent theory and memory-color idea underpin modern accounts of stable surface color.

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