Optical color is the color that the optic nerves' perception creates. That is, when brush strokes of different color are juxtaposed, the eye perceives them as one color. For example, when red and blue are placed side-by-side, the optical color becomes purple.
An Impressionist, George Seurat was a painter who made great use of optical color. His style called Pointillism, employed the treatment of dots of primary colors, which the human eye blended into the secondary color. In his painting, Sunday Afternoon on the Grande Jatte, for instance, the green of the tree tops is created by the juxtaposition of the primary colors of blue and yellow. In another painting, Nude in the Sunlight, August Renoir uses short, quick brushstrokes of several colors to create the play of light upon his subject, and the optical colors are different from the individual brushstrokes. Thus, optical color well served the Impressionists, who wished to give a vivid impression of how something happens to look at a particular moment.