Subtractive Color Theory

In color, the production of intermediate colors by mixing the subtractive color primaries, or colorants that correspond to cyan, magenta, and yellow. Colored substances differ from colored light in that it is their selective absorption of light of certain wavelengths that imparts their color. For example, a cyan pigment absorbs red light, so it appears blue-green; a magenta pigment absorbs green light, so it appears reddish; a yellow pigment absorbs blue light so it appears yellow. The combination of all three of these pigments tends to produce black, at least in theory. (Additive color theory involves the use of light—rather than colorants—which, although producing roughly the same effect, works on a very different principle; see Additive Color Theory.)

Inks, dyes, and other materials used in printing, for example, produce many of the colors discernible to the human eye by means of subtractive colors. Varying the amounts of the three primaries (and, in printing, the use of black) produces all the shades in between. It should be noted, however, that the color a printed or dyed material is perceived as will depend upon the color of the light used to view it. Under normal white light, a yellow ink will look yellow, since the red, green, and blue light (or the additive color primaries) are all present in equal proportion, and the blue light is being absorbed by the colorant, the light reflecting back consisting of red and green light, thus mixing to appear yellow. If the yellow ink were viewed using only a green light, it would appear green, since there is no blue light present, and only the green will be reflected back to the eye.

Color computer monitors display colors utilizing the additive colors, while inks to be printed utilize the subtractive colors. It is the difference between the additives and the subtractives which makes color reproduction originating on a computer screen difficult.

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