The study of color is carried on by two principal methods: the spectroscopic, where the colors are partially separated as a continuous band by a regular variation in their indices of refraction, the colors gradually merging into each other by overlapping in opposite directions; or by absorption, where a color is developed by absorbing its complementary, and is isolated as a single or complex color. This latter is nature’s own method.
It is necessary to touch on some theoretical differences which exist between Scientists and Artists, as to which are Primary colors, as confusion of this character impedes investigation. Scientists adopt Red, Green, and Violet as Primaries, regarding all other colors as mixtures of these; whilst Artists and colorists adopt Red, Yellow and Blue as the Primaries, and all other colors as made from them.
The theory of the Scientists is based on the phenomena developed by mixing colored lights taken from different parts of the spectrum. This is a method of synthesis, each added color being a progressive stage towards the complexity of white light. In this case the color developed is that of the preponderating ray of a complex beam. The theory of the Artists is based on the phenomena developed by mixed pigments. This is a method of analysis, tending towards ray simplicity, each added pigment reducing the complexity of the color developed by its power of selective absorption.
The theoretical differences between the two schools appear to have arisen from supposing that a given color developed by the two methods should correspond; but considering the differences in their ray composition, this would be impossible, for although both may be describable by one general color term, as for instance a Red, they would be of two varieties. It remains to be shown that one theory may cover both sets of phenomena.
The Red, Green, and Violet theory appears to be based on two principal assumptions: first that there are only three fundamental colors; and second that the rays taken from different color areas are pure colors. Both assumptions are open to question. In regard to the first, there is no difficulty in isolating six colors; and as to the second, it can be demonstrated that the colors do overlap in every part, with a double overlapping in the middle colors, and are therefore not simple but complex.