Keep in mind that the additive primaries-red, green, and blue-are the basic starting colors from which all other colors of light can be created. When you are working with light, the additive primaries produce all the other colors; however, they will not do this as dyes or pigments; for example, blue and green dyes cannot be mixed to produce cyan, though blue and green light can.

For dyes and pigments, another set of primaries are needed. This other set of primaries happens to be yellow, cyan, and magenta. Dye couplers are what form the colors within a color print (or film). The dye primaries-cyan, magenta, and yellow-can be used separately or superimposed (mixed), one image over the other, to produce other colors; that is,

cyan + magenta = blue;

magenta + yellow = red; and

yellow + cyan = green.

The colorant primaries-cyan, magenta, and yellow-are called the subtractive primaries because they subtract certain colors from the light falling on them.

Anything that is colored is subtracting something from white light; that is, an object appears a certain color because it is subtracting or absorbing a certain other color or colors from the light falling upon it; for example, an object that appears red subtracts green and blue (cyan) light; green subtracts red and blue (magenta) light; blue subtracts green and red (yellow) light; magenta subtracts green light; cyan subtracts red light; and yellow subtracts blue light.

Figure 12-2. Color star.

This whole concept of color by subtraction may seem confusing at first, but if you accept this concept, it will suddenly become very clear. Color printing is built around color by subtraction.