As discussed on the previous page, the three secondary colors produced by mixing any two primary colors of light form cyan, magenta, and yellow (CMY), otherwise known as the subtractive colors, or colors used in the subtractive mixing process.

The subtractive process is used in mixing printing inks, as well as dyes, paints, plastics, or other physical materials in which pigments are mixed with a base material.

Mixing pigments results in a subtraction of the reflected light from a surface. This is because when pigments are mixed to form another color, the resulting color combines the absorption characteristics of both colors, and is darker rather than lighter. More of the colors' wavelengths are absorbed in the mixed color than in either original color, and not reflected back to the eye.

Combining two of the subtractive colors by mixing pigments theoretically should produce one of the primary colors of light: red, blue, or green (RBG). In theory, a combination of cyan and magenta pigments should produce blue, magenta and yellow pigments should produce red, and cyan and yellow pigments should combine to produce green. However, the pigments used to make the colors are typically not pure, resulting in dull colors that are not what theory would suggest. This problem is compensated for by adjusting the proportions of pigments mixed to produce the desired color.

When cyan, magenta, and yellow are combined, they theoretically form black. In practice, however, the impure nature of pigments used to make the colors results in a dull brown or gray. An additional pigment, black (K), is added to ensure the combination appears as a true black and to deepen shadow areas.

Subtractive color mixing is used in the 4-color printing process, consisting of inks in the colors cyan, magenta, yellow, and black (CMYK). The four colors are printed onto a surface, usually white or a light color. Many desktop printers also use this model to reproduce colors on a surface.

When we view the final printed piece, the light from the surface of the material is reflected back to the eye through the layers of pigments that have been applied to the surface. Each layer subtracts bandwidths of light, and combines with the others to create an illusion of multiple colors.

In 4-color process printing, the image is separated into each of the four process colors. These color separations are used to make plates for the presses to run each ink color, one plate per color. The plates are screened into a pattern of tiny dots, and the angles of each color plate are set differently, to produce a pattern called a rosette, which gives the illusion of color transitions. If any of the screened plates are misaligned or out of register, a moire pattern, a mottled and visually discontinuous appearance, results instead.

Some process printing methods use more than four colors, adding additional ink colors into the process to increase the range of colors. Another method, spot color printing, is different from process printing because it involves applying solid layers of ink in pre-mixed combinations of pigments that typically allow little or no reflection of the surface. In this method, only the colors from the flat layers of pre-mixed ink are reflected back. The background surface is visible where no ink has been applied. This method is often used for budget printing, or in combination with process printing, to add a layer that most closely duplicates a specific color.