When two or more tertiary colors are mixed together, the result is a color gray. Such a gray is to be distinguished from a neutral gray, which is a mixture of black and white pigments. Individual color names have not been given to the color grays, because the proportion of each tertiary color that is used in the mixture can vary widely.
Warm and Cool Colors
The twelve colors of the spectrum and the various color grays may be classed broadly as either warm or cool colors. Red, yellow, and orange, which give the effect of fire or heat, are warm colors. Blue, which is the color of ice, and its related colors, green and violet, are classed as cool colors. Similarly, a gray in which a warm color predominates can be called a warm gray; a gray in which a cool color predominates can be called a cool gray.
Advancing and Receding Colors
Warm colors are commonly called advancing colors; that is, the warm colors attract your eye and appear more prominent and closer than do the cool, or receding, colors. The degree of advance or recession depends upon the value of the color. A dark red is less noticeable than a light red, for instance. Grayed or neutralized colors are the least noticeable of all colors.
Warm, advancing colors, particularly in the lighter variations of the hues, have a tendency to increase the apparent size of an object. A hue containing red or yellow is likely to add an appearance of greater bulk. Cool colors, particularly in the darker shades, make objects appear smaller and heavier in weight.
Complementary colors are those colors which, taken together, include all three primary colors. Thus the complement of red is green, which is made up of blue and yellow. The complement of yellow is violet, made up of blue and red. And the complement of blue is orange, made up of red and yellow.
Analogous colors are related colors. Related colors share a common color. Thus, blue, blue-violet, and blue-green are all related colors, because they share the common color blue. Red-orange, orange, yellow-orange, yellow, yellow-green, and green are related colors that form a color analogy with the common color yellow. A color analogy may include any number of related colors from three to six, but there is usually the ideal number. By referring to the twelve-color spectrum, you can see that a color analogy include seven colors, because a seventh color would be a complementary or contrasting color.