=Complementary Colors.=--Two colors are said to be complementary to each other when they together contain the three primaries in equal strength. Green, for instance, is the complementary of red, for it contains yellow and blue; orange (yellow and red) is complementary to blue; and purple (red and blue) is complementary to yellow.
The knowledge of complements of colors is very important to the painter, for all the effects of color contrast and color harmony are due to this. Complementary colors, in mass, side by side, contrast. The greatest possible contrast is that of the complementaries.
Complementary colors mixed, or so placed that small portions of them are side by side, as in hatching or stippling, give the tertiaries or grays by the mixing of the rays.
=The Law of Color Contrast.=--"When two dissimilar colors are placed in contiguity, they are always modified in such a manner as to increase their dissimilarity."
=Warm and Cold Colors.=--Red and yellow are called warm colors, and blue is called a cold color. This is not that the color is really cold or warm, of course, but that they convey the impression of warmth and coldness. It is mainly due to association probably, for those things which are warm contain a large proportion of yellow or red, and those which are cold contain more blue. There is a predominance of cold color in winter and of the warm colors in summer.
From the primaries various degrees of warmth and coldness characterize the secondaries and tertiaries, as they contain more or less proportionately of the warm or cold primaries.
In contrasting colors these qualities have great effect.
=Color Juxtaposition.=--In studying the facts of color contrast and color juxtaposition you will find that two pigments, if mixed in the ordinary way, will have one effect; and the same pigments in the same proportions, mixed not by stirring them into one mass, but by laying separate spots or lines of the pigment side by side, produce quite another. The gain in brilliancy by the latter mode of mixing is great, because you have mixed the _color rays_, which are really light rays, instead of mixing the _pigment_ as in the usual way. You have really mixed the color by mixing _light_ as far as it is possible to do it with pigment. You have taken advantage of all the light reflecting power of the pigment on which the color effect depends. Each pigment, being nearly pure, reflects the rays of color peculiar to it, unaffected by the neutralizing effect of another color mixed with it; while the neutralizing power of the other color being side by side with it, the waves or vibrations of the color rays blend by overlapping as they come side by side to the eye; and so the color, made up of the two waves as they blend, is so much more vibrant and full of life.