Complementary colors are pairs of opposite colors. What is meant by opposite can be different between color science, art, and printing.

In color science, "complementary colors" are colors opposite to each other on the color wheel. Primary colors and secondary colors are paired in this way:

• red and cyan ( red   cyan ), where cyan is the mixture of green and blue
• green and magenta ( green   magenta ), where magenta is the mixture of red and blue
• blue and yellow ( blue   yellow ), where yellow is the mixture of red and green

Along with these pairs, there is another pair of complementary colors: the basic color and the tertiary color made by mixing two other complementary colors.

• black and white ( black   white ), where white is the mixture of red, green, and blue

If a person stares at a single color for about a minute then looks at a white surface, an afterimage of the complementary color will appear. This is because of eye fatigue.^[1] For example, if the person stares at a red color, the photoreceptors (cells in the eye which catch colored light) for red light in the retina (the back part of the eye) become fatigued. When photoreceptors are fatigued, they are less able to send information to the brain. If the person then looks at white light, all photoreceptors will send information. Because the photoreceptors for red light are fatigued, the information they send will not be as strong as the information about the other colors, and the illusion of seeing the complementary color, cyan, is made.

Because of the limited range of colors that was available throughout most of the history of art, many artists still use a traditional set of complementary pairs, including:

• red and green
• blue and orange
• yellow and purple

The complement of each primary color (red, blue, or yellow) is roughly the color made by mixing the other two in a subtractive system (red + blue = purple; blue + yellow = green; red + yellow = orange). When two complements are mixed, they produce a gray or brown.

The use of complementary colors is an important aspect of art and graphic design. This also extends to other fields such as contrasting colors in logos and retail display. When placed next to each other, complements make each other appear brighter. On an artistic color wheel, complementary colors are placed opposite one another. Although these artistic complements are not complements under the scientific definition, most artistic color wheels are laid out roughly like the HSV color wheel.

1. ↑ "Color & The Absorption Spectrum". Archived from the original on February 23, 2007. Retrieved January 14, 2007.