PDF colour: RGB, CMYK and why prints look different

Colours that glow on a monitor can print flat and muddy. The cause is that screens and printers speak different colour languages.

RGB is for screens

Monitors mix red, green and blue light, so on-screen PDFs use RGB. It produces vivid, saturated colour — including bright blues and greens a printer cannot reproduce.

CMYK is for print

Printers layer cyan, magenta, yellow and black ink. That gamut is smaller, so a neon RGB colour gets mapped to the nearest printable value — which can look duller than the screen promised.

Getting predictable prints

For professional printing, convert to CMYK with the printer's colour profile (a PDF/X workflow), and preview with soft-proofing. For office printing, do not worry — modern printers manage the conversion well enough.