Handbook

CMYK – on press today.
RGB – on screen for me.

The CMYK colour model (process or 4-colour), is what’s called a subtractive colour model used in colour printing and also describes the process itself. CMYK refers to the four inks used in some colour printing: Cyan, Magenta, Yellow and Key black. Interestingly, the ‘K’ is not a Latin or Greek letter reference for black. In this case it means ‘Key’ as in the other colours ‘key’ into the black printing plate.

CMYK works by somewhat or completely masking colours on a lighter background. The ink reduces the light that would otherwise be reflected. Hence being called a subtractive colour model.  

Moving right along to the screen, we have the RGB colour model, which is an additive colour model.  Red, Green and Blue light are added together in various ways to reproduce a broad colour array. The RGB colour model is for the sensing, representation and display of images in electronic systems, like televisions and computers and, now, digital photography. As an additive colour model, white is the “additive” combination of all primary coloured lights, while black is the absence of light. In the CMYK model, it’s the reverse: white is the natural colour of the background (paper, let’s say), and black is created from a full combination of coloured inks.