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 darken into black. If the remainder is only partially inactive, then the color loses its energy by mixing with gray. If the activity of the retina is divided without a remainder, or if the remainder is active, then a color and its spectrum (afterimage) are bright or pale. When such a color and its spectrum are united, then the eye sees pure light or white. For example, the mixture of bright or pale red and green on the same retinal spot results in the impression there of light or white. White cannot be produced by mixing colored pigments. With colors