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. (See Diagram III.)
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.
22. In the use of one color with another of contrasting character the question frequently arises, what proportion of each should be used to obtain the best effect? Illustrative color books show usually samples of color of the same size, leading one unconsciously to the error that contrasting colors should occupy the same surface dimensions.
23. In every room there must be a prevailing or dominant color, and the use of a contrasting color must be limited to proportions which give simply a pleasing emphasis. Let us assume that a room has a deep frieze pronouncedly green. To treat the rest of the wall in red of a direct contrast would be ineffective.
24. If a rule can be applied we would say that no strong normal color should be used in large surfaces. If we were dealing with pigments we would say that if one-sixth of a side-wall is devoted to a frieze in green, the balance of the wall space should be treated with the same amount of red, mixed with the same amount of gray.
25. For a room that is small and well lighted the fresh tints are not as desirable as the gray shades or tertiaries in conjunction with secondaries.