On Vision and Colors are, however, nonessential properties that differ according to the type of light-refracting substance that is used. The top of the upper image is violet. Below the violet is blue. The bottom of the lower image is orange. Above the orange is yellow. In this way, along with the white disk and the black background, four prismatic colors appear: violet, blue, yellow, and orange. This is in disagreement with Newton's claim that there are seven prismatic colors. As the upper image overlaps black, it is seen as violet. Where it overlaps white, it is seen as blue. As the lower image
On Vision and Colors that were exhausted by the whiteness become completely inactive. The retinal positions that had been rested are now easily stimulated. This explains afterimage (physiological spectra). Both Goethe and Schopenhauer use the word "spectrum" [Spektrum], from the Latin word "spectrum" meaning "appearance" or "apparition," to designate an afterimage. If, instead of white, we stare at yellow, then the afterimage, or physiological color spectrum, is violet. Yellow, unlike white, does not fully stimulate and exhaust the retina's activity. Yellow partially stimulates points on the retina and leaves those points partially unstimulated. The retina's activity has been qualitatively divided and separated into two