Bird in a Cage produces a color afterimage in the eye. By staring at the red bird for 15 to 30 seconds and then switching views to a white wall, visitors will see an image of the bird in its complementary color (in this case, blue-green). A green bird produces a magenta afterimage. This effect results from our eyes adapting to one particular color, so that when we suddenly look at something else (like a white wall), we see everything but that color.