We mentioned the color wheel during our descriptions of the HSB and HSL color models, and we will come across it regularly in the form of various sliders and adjustments. The color wheel arranges hues in approximately the same order as a rainbow. In the color wheel, yellow lies opposite blue, and green lies opposite magenta.

Colors that lie diametrically opposite one another in the color wheel are called complementary colors. These color pairs form maximum visual color contrast, so it is useful to know the complementary colors of basic red, green, blue, cyan, magenta, and yellow tones when composing your images.

Figure 3-37. The color wheel showing two examples of complementary colors

This knowledge can also help in other situations. For example, if an image has a color cast, you can get rid of it by either reducing the color of the cast or by increasing the intensity of its complementary color.

Offset printing uses cyan, magenta, and yellow – i.e., the complementary colors to those in the RGB color model – as base hues (Figure 3-38). Remember, the RGB model mixes emitted primary colored red, blue, and green light, whereas in the CMYK model, some of the white light is absorbed and the rest is reflected. This makes the CMYK model ideal for print applications. Complementary color sliders are the base tool in the Photoshop Color Balance correction dialog (Figure 3-39).

Figure 3-38. The RGB model as complementary to CMY

Figure 3-39. The Color Balance correction dialog