CMYK refers to the printing inks used in four-colour process printing, being Cyan, Magenta, Yellow and Black. These are the only colours used to produce full-colour photographs and designs.

On a press, the colours are combined and printed to emulate a wide number of other colours. If you look carefully at a printed colour photograph in any magazine or book, you'll see that it's made up of rows of tiny dots of each of the four colours called a halftone screen. The dots work together, at different angles, to fool your eye into seeing a full spectrum of colours...