Yellow, Cyan, Magenta, Black or CMYK
The primary pigment colors used in 4 color process printing and most desktop publishing programs. CMY are the subtractive primary colors and are used to reproduce full color on the printed sheet.
If these pigments are combined in equal amounts, black is supposed to be produced, but because of imperfections with the pigments, a muddy brown color is produced.
For that reason, black (represented by K) is added to give definition to color reproduction and to create bolder text.