“Once, toward evening, I found myself in a smithy just as the glowing metal was laid on the anvil. After gazing intently at this activity for a time, I turned and happened to look into the open doorway of a coal bin. At that moment an enormous purple form floated before my eyes; when I glanced over at a light-colored wooden wall the phoenomenon appeared half in green, half in purple depending one whether the background was light or dark. At the time I made no note of how this phenomenon faded.

The phenomena associated with the fading of an extremely bright bounded form also occur when the entire retina has been blinded by light. The purple color seen by those who have been blinded by snow belongs in this category, as does the uncommonly beautiful green color seen in dark objects after we gaze at a sheet of white paper lying in the sun. A more exact investigation of these phenomena will await the younger researcher whose eyes can still bear some hard use for the sake of science.”

—Johann Wolfgang von Goethe, from his Farbenlehre, or Theory of Color, 1808. Translated from the German by Douglas Miller, 1988.