These are the four process colours often used when printing (CMYK is an abbreviation of cyan, magenta, yellow and key - black).
A printing press uses dots of ink or toner to create the image from these four colours.
Most devices with screens (monitors, TVs and smartphones for instance) display images in RGB (Red, Green, Blue) and not CMYK. This can cause an image on screen to look very different on paper than it does on screen. This is because RGB is additive, while CMYK is subtractive. What this means is:
- RGB colours are added to a black canvas to build an image
- CMYK colours are added to a white canvas to remove other colours from the visual spectrum
As a result you'll find a lot of colours you can create in a design on screen (neon and other bright vibrant colours in particular) appear much duller and muted on paper.
We advise that you always set your software to use a CMYK colour profile when designing for print to avoid problems with colour conversion.