Color Complements and AfterImages
Complementary colors are central to color matching (color harmony)..
An afterimage is a visual image that persists after the visual stimulus causing it has ceased to act.
In 1839 artist and scientist Michel Eugène Chevreul first defined complemenrtary colors in terms of a color and its induced afterimage. Such an afterimage would appear, for instance, when a white card with a red square was viewed for perhaps half a minute, and then replaced immediately with a white card. The viewer would temporarily see a faint cyan square.
Later, starting in the 1930s, complementary colors came to be defined as two colors of appropriate intensity that when mixed produced a particular achromatic color (ie white or gray, depending on the light source). That two colors could produce white had been known at least as early as 1673 when Isaac Newton wrote "I have produced White out of two colours alone, and variously, as out of Orange and full Blew, and out of Red and pale Blew, and out of Yellow and Violet...".
Up until a few years ago, the dominant explanation of afterimages was that certain "opponent color" receptor cells in the eye would become fatigued upon viewing a color continuously, and that with the removal of that color from view, those cells would erroneously register the "opponent" color. But recent research has demonstrated that the brain plays a dominant role in the formation of afterimages, and that the required neural processes are also essential to other visual functions.
A Demonstration of AfterImages
Select a color, and then focus on the slight movement of the cross in the center of the image. Soon you should become aware of a colored dot moving around the ring of dots, that dot having a color complementary to the selected color, albeit somewhat fainter (less saturated).