Color printing typically uses ink of four colors: cyan, magenta, yellow and key (black).

When CMY “primaries” are combined at full strength, the resulting “secondary” mixtures are red, green and blue. Mixing all three gives an imperfect black.

The CMYK color model(process color,four color) is asubtractive?color model, used incolor printing, and is also used to describe the printing process itself.CMYK refers to the four inks used in some color .

The "K" in CMYK stands for key because in four-color printing, cyan, magenta and yellow printing plates are carefullykeyed,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.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.

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.

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,unsaturatedand dark colors are produced by using black ink instead of the combination of cyan, magenta and yellow.