17. Diagram III is of the utmost value to the colorist, illustrating not only the composition of color, but showing the origin of each secondary from the two primaries, the origin of each tertiary from two secondaries, and of each quaternary from two tertiaries. It shows by groupings the harmonies of analogy or related colors; also the harmonies of contrast: By moving on the board one color on one line to another color upon another line, like the moving of a knight in a game of chess,
18. A harmony of contrast means the utilization of a primary color with its complementary, or a color in conjunction with another color in no degree related: a primary with a secondary. But when we soften these contrasting colors by the addition of white we have in the lighter tints a scale of chroma that is a form of analogy.
19. All combinations of secondary and tertiary colors, while apparently harmonies of contrast (the tertiary being made by the composition of two secondaries), constitute, in fact, contrast analogies, because by analysis we find that all tertiaries possess color components occurring in the apparently contrasting secondaries.
20. The harmony of contrast, literally, can only occur in the pure primary colors juxtaposed to the pure secondary colors, for in no case does the color formed by the combination of the two primaries have anything in common with the third primary; while a tertiary composed of two secondaries invariably has qualities possessed by the third secondary.
21. In a room which is small or dark, the light tints in harmonies of analogy are advisable.