The illustration on this page is an enlarged section of a book illustration. The book illustration is typical result of the 4-colour (CMYK) printing process. The enlarged section demonstrates how the cyan, magenta and yellow inks combine. (This particular section doesn’t happen to need the black ink.)
In one region a more-or-less pure red is produced by a combination of magenta and yellow inks. In another region, a bluish cyan is produced by combining some magenta with the cyan. In the third region, purple colour is produced by combining cyan with a larger quantity of magenta.
A very slight misalignment during the original printing process also produces some revealing combinations. Wherever the cyan and magenta dots overlap, the result is blue. Where red and cyan regions overlap, the combination of cyan, magenta and yellow produces a dark brown that may appear black on this computer monitor.