colorillusion

A color illusion (also spelled colour illusion) is a perceptual phenomenon in which an observer’s experience of a surface’s color differs from its physical spectral properties because of contextual, lighting, or neural processing factors. Such illusions reveal how the visual system interprets wavelength information from the environment rather than reporting it verbatim.

Common types include simultaneous contrast, where adjacent colors alter perceived hue or brightness; color constancy, in which surfaces appear to maintain stable color under changing illumination; afterimages, produced by photoreceptor adaptation; and metamerism, where different spectral distributions appear identical. Classic demonstrations include the checker-shadow illusion and widely publicized examples such as “the Dress,” which emphasize how assumptions about illumination and scene geometry influence color perception.

Mechanisms underlying color illusions involve interactions at multiple stages of the visual system: photoreceptor responses in the retina (cone types), opponent-process encoding, lateral inhibition, and cortical processing that factors contextual cues and prior expectations. Psychophysical experiments, computational models, and neuroimaging studies are used to investigate these processes.

Color illusions have practical implications for art, design, display technology, camouflage, and color reproduction, where perceived color often matters more than measured spectra. They also inform theories of visual perception by demonstrating the brain’s constructive role in interpreting sensory input.