Stare at the red box for a minute.
(Or use the arrow keys or touch the right or left edge of the window.)
After you stare at a color for a while, if you look at a blank white area, you may see an afterimage in the complementary color. The purpose of this exercise is to see what those complementary colors are, and under what conditions you can see them.
In traditional art theory, the complementary colors are:
According to modern color theory, the complementary colors are slightly different:
Brighter and lighter colors may create more vivid afterimages. Do you agree?