On Vision and Colors from a prism, however, the production of white can be demonstrated by using a mixture of colored light from each of the three main pairs of complementary colors: red – green, orange – blue, or yellow – violet. White can be produced from two complementary opposite colors when both of the external causes of the colors excite the same retinal place at the same time. Newton claimed that white could be produced by the aggregation of his seven prismatic colors. He erroneously considered color to be in light instead of in the eye. White is the result of the combination
Complementary colors effect that colors have upon each other had been noted since antiquity. In his essay "On Colors", Aristotle observed that "when light falls upon another color, then, as a result of this new combination, it takes on another nuance of color." Saint Thomas Aquinas had written that purple looked different next to white than it did next to black, and that gold looked more striking against blue than it did against white; the Italian Renaissance architect and writer Leon Battista Alberti observed that there was harmony ("coniugatio" in Latin, and "amicizia" in Italian) between certain colors, such as red–green and