To help understand color theory, draw a color star and use it through the color process (fig. 12-2). With a color star, both additive and subtractive color effects can be illustrated.

The color star shows how colors can be mixed. Any two primaries (colors) on opposing points of a given triangle, when mixed, will produce the color between them; for example,

green and red = yellow;

yellow and cyan = green; and

green and blue = cyan.

Just as important, the color star shows the colors that will neutralize each other. These colors are called complementary colors and are located across from each other; that is yellow is complementary to blue; magenta is complementary to green; and cyan is complementary to red.

Thus yellow neutralizes blue, blue neutralizes yellow, red neutralizes cyan, cyan neutralizes red, and so forth.

When colors are neutralized, the results are grays or blacks. That is called neutral density. The neutral density may be either full or partial, depending on the relative strengths and amounts of the neutralizing colors; for example, equal amounts of blue and yellow produce neutral density. A weak blue and a strong yellow yields a grayish yellow.

The information on the color star can be applied directly to color printing and color filtration. The filters used in color printing subtract colors from the light source of the enlarger before it reaches the color printing paper; for example, to subtract green from the light, you use a magenta filter, or to subtract blue, you use a yellow filter or vice versa.

In color printing, filters are always used to subtract a particular color. You can determine which filter subtracts a given color from the light source of the enlarger by finding its opposite or complementary color on the color star. For example, you want to subtract green from the light. First, find green on the color star. Next, locate the complementary color of green by looking across from it. You have located the color, magenta; therefore, to remove green from the light source, you must addmagenta filtration in the enlarger.

The basic overview of the principles of color photography applies directly to color printing. If you need additional review of light and color principles, refer to chapter 1 of this training manual. The remainder of this chapter should help you get a better understanding of color printing and provide the information you need to make good, professional quality color prints.