CMYK is an abbreviation for cyan, magenta, yellow, and black (or key). These ink colors are used in four-color process printing. Most home printers are CMYK printers. Some very old, low-end consumer printers are CMY with no black, but these are rare.

+ makes Blue + makes Red + makes Green + + makes Brown or gray + + + makes Deep black

Some CMYK mixtures

Some photo printers use a variation known as CcMmYK or CcMmYKk. These printers use two shades of each ink so that colors can be produced more accurately. The uppercase letters stand for the regular pigment (which is a bit deeper than regular cyan or magenta) and the lowercase letters stand for the lighter pigment, which is about a 20% version of regular cyan and magenta. Another standard still (known as Hexachrome) uses CMYK plus green and orange inks.

Here is a rough simulation of what an image looks like printed in the different ink mixtures.

Original	CMY	CMYK
Hexachrome	CcMmYK	CcMmYKk

For technical details on how these simulations were made, click here.

Sample image: detail of The Arnolfini Marriage, painted by Jan van Eyck in 1434.