opponent process theory

Utilizing the additive color mixing model, blue is in opposition to yellow, red to cyan and green to magenta. We do not see reddish cyan nor greenish magenta. Complimentary afterimages also conform (loosely) to these pairings.

AFTER IMAGE

To see an afterimage of the medicinal buddha: stare at it for a full thirty seconds, then immediately gaze at the white space on the right or a white wall...

The trichromatic theory was validated when the three types of retinal cones were discovered and described. The opponent process theory was resurrected by Edwin Land (the inventor of Polaroid) in the 1970s. Land demonstrated that the retina and the cortex of the brain is a single optical system. He could this the retinex. The current view is that the trichromatic and opponent theories are quite compatable. Color opponency seems to operates at a deeper level of the neural processing hierarchy.

Although the Young-Helmholtz trichromatic theory was based on a broad swathe of contemporary experimental evidence, it could not explain the phenomenon of complimentary afterimages or the reason why we never see reddish-green or bluish yellow.

Austrian physiologist, Ewald Hering (1834-1918) proposed that the visual process included the generated signals in opposing pairs. He noticed that his 16 sector color wheel could be divided into opposing pairs: yellow-blue, red-green and white-black.