Many colors can be separated into their component primaries. In light the additive primary colors are red, green, and blue. Magenta light, for instance can be separated into its two components, red and blue. In pigments, the subtractive primaries are cyan, magenta, and yellow. Gree ink, for example can be separated into its components, cyan and yellow. When printing with inks, black is also added to the other three primaries as it's difficult to get a rick black ink by mixing the subtractive primaries. Most color printing is therefore done with four colors - cyan, magenta, yellow, and black. These four color printing images are often called "color separations."
