Complementary color

Complementary colors are pairs of colors which, when combined, cancel each other out. This means that when combined, they produce a grey-scale color like white or black. When placed next to each other, they create the strongest contrast for those particular two colors. Due to this striking color clash, the term opposite colors is often considered more appropriate than "complementary colors".

Which pairs of colors are considered complementary depends on the color theory one uses:

On the traditional color wheel developed in the 18th century, used by Claude Monet and Vincent van Gogh and other painters, and still used by many artists today, the primary colors were considered to be red, yellow, and blue, and the primary–secondary complementary pairs are red–green, orange–blue, and yellow–purple.

In the traditional representation, a complementary color pair is made up of a primary color (yellow, blue or red) and a secondary color (green, purple or orange). For example, yellow is a primary color, and painters can make purple by mixing of red and blue; so when yellow and purple paint are mixed, all three primary colors are present. Since paints work by absorbing light, having all three primaries together results in a black or gray color (see subtractive color). In more recent painting manuals, the more precise subtractive primary colors are magenta, cyan and yellow.

Complementary colors can create some striking optical effects. The shadow of an object appears to contain some of the complementary color of the object. For example, the shadow of a red apple will appear to contain a little blue-green. This effect is often copied by painters who want to create more luminous and realistic shadows. Also, if you stare at a square of color for a long period of time (thirty seconds to a minute), and then look at a white paper or wall, you will briefly see an afterimage of the square in its complementary color.

Placed side by side as tiny dots, in partitive color mixing, complementary colors appear gray.

The RGB color model, invented in the 19th century and fully developed in the 20th century, uses combinations of red, green, and blue light against a black background to make the colors seen on a computer monitor or television screen. In the RGB model, the primary colors are red, green and blue. The complementary primary–secondary combinations are red–cyan, green–magenta, and blue–yellow. In the RGB color model, the light of two complementary colors, such as red and cyan, combined at full intensity, will make white light, since two complementary colors contain light with the full range of the spectrum. If the light is not fully intense, the resulting light will be gray.

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Wikipedia