CMYK

CMYK — Cyan, Magenta, Yellow, and Key (black) — is the four-colour subtractive process used for full-colour printing. Files supplied as RGB (the additive model used by screens and cameras) are converted to CMYK at prepress, with a colour profile that matches the press, ink, and substrate.

Also called: four-color process · 4-color process · process colour printing · CMYK printing · RGB vs CMYK

In depth

Print presses build colour by overprinting four translucent inks in halftone dots. Combinations of cyan, magenta, yellow, and black produce the visible colour gamut. Black is added as a separate "key" plate because layering CMY alone produces a muddy dark brown rather than a clean black, and uses three times the ink to do it.

The challenge in colour management is that screens use additive RGB (red, green, blue light) and produce colours that CMYK ink on paper cannot reach — bright saturated greens and electric blues, in particular. The conversion from RGB to CMYK has to make choices about how to map out-of-gamut colours into the printable range. A colour profile (ICC profile) specific to the press, ink, and stock describes those choices so the result is predictable.

For brand-critical work, Pantone spot colours can be printed as a fifth (or sixth, seventh) ink alongside CMYK. This is more expensive (extra plate, extra wash-up) but produces exact brand colours that CMYK cannot reach.

Common questions

My PDF looks great on screen but dull when printed — why?+
Almost always an RGB-to-CMYK conversion issue. Screen displays show RGB at near-100% saturation; CMYK on paper cannot reach the same saturation in greens, oranges, and purples. Convert in your design tool with the printer's recommended profile and proof on a calibrated screen or a press proof.
Should I supply files as RGB or CMYK?+
Most modern print workflows accept both. Supplying as CMYK with the printer's recommended profile gives you direct control over colour decisions. Supplying as RGB delegates that conversion to the printer's preflight, which is fine for non-brand-critical work.

Related terms

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