Four-color printing is one of the types of printing. It is a method for color printing with four colors of yellow (Y), magenta (M), cyan (C) and black (BK). In theory, four-color printing can obtain tens of thousands of colors, with Y, M, C and BK four colors combined without repetition. Monochrome-four kinds of Y, M, C and BK; two colors-six kinds of Y+M, Y+C, Y+BK, M+C, M+BK, C+BK; three colors-Y+M +C, M+C+BK, Y+C+BK, Y+M+BK; four colors—Y+M+C+BK, a total of fifteen colors. In color printing, the size of the "dot" is used to indicate the depth of the color. In theory, the "dot" can be divided into 22 levels, calculated according to the arrangement and combination formula Cm·g, and C14·221+C24·222 can be obtained +C34·223+C44·224=279840 (species) color.

In fact, due to the deformation error of the "dot" in the printing process and the limitation of the visual recognition threshold, the four-color printing can obtain much less color than in theory.