<P> The "K" in CMYK stands for key because in four - color printing, cyan, magenta, and yellow printing plates are carefully keyed, or aligned, with the key of the black key plate . Some sources suggest that the "K" in CMYK comes from the last letter in "black" and was chosen because B already means blue . However, some people disagree with this because C for Cyan is classed as the blue when printing in CMYK format . Some sources claim this explanation, although useful as a mnemonic, is incorrect, that K comes only from "Key" because black is often used as outline and printed first . </P> <P> The CMYK model works by partially or entirely masking colors on a lighter, usually white, background . The ink reduces the light that would otherwise be reflected . Such a model is called subtractive because inks "subtract" brightness from white . </P> <P> In additive color models, such as RGB, white is the "additive" combination of all primary colored lights, while black is the absence of light . In the CMYK model, it is the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks . To save cost on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta, and yellow . </P> <P> With CMYK printing, halftoning (also called screening) allows for less than full saturation of the primary colors; tiny dots of each primary color are printed in a pattern small enough that humans perceive a solid color . Magenta printed with a 20% halftone, for example, produces a pink color, because the eye perceives the tiny magenta dots on the large white paper as lighter and less saturated than the color of pure magenta ink . </P>

The primary colors of pigment are yellow magenta and