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What Is CMYK?

What Is CMYK?

Read Time: 6 Minutes


17 Aug 2017

If you’ve ever printed anything with a commercial print service, it’s likely you’ve heard the term CMYK. But what does it stand for, and why is it important?

CMYK: The Basics

The acronym stands for Cyan, Magenta, Yellow, and Key: those are the colours used in the printing process. A printing press uses dots of ink to make up the image from these four colours.

‘Key’ actually means black. It’s called Key because it’s the main colour used to determine the image outcome. Black ink provides depth and shading, whereas the other colours create different colours on the spectrum depending on how they are mixed. For example, cyan and yellow create a green when one is overlaid on the other.

There’s some argument regarding the origin of ‘Key’ to mean black. Some people say it’s because representing black with ‘B’ could confuse it with ‘blue’, but this is unlikely. It may be because the black plate is the ‘key’ plate on a printing press that aligns the other three colours to it (so the layers match up perfectly for the final image). This means any colour plate, in theory, could be the ‘K’ in this process, if black were not being used.

A further argument suggests that ‘Key’ refers to the very old presses waaayyy back in 1843 that used screw keys to determine the amount of ink required to achieve the desired end result.


Your computer screen works in RGB (Red, Green, Blue) and not CMYK. It might seem that this doesn’t make a difference to the final product when you’re designing something, but it does!

A colour monitor that isn’t set up to view CMYK will show you different colours to the ones that may be printed. This is because the RGB spectrum is much, much broader than CMYK, so colours can be created in this palette that won’t be available in CMYK.

There is a very clear differentiation between RGB and CMYK in the way the colours work. 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.

Why Printers Use CMYK

Some commercial printers will print in RGB, but most (including instantprint) will only print in CMYK. This is because CMYK is easier to standardise, thanks to the spectrum of colours available. There are so many minute variations possible in RGB that it is nigh on impossible to guarantee consistency of colours across a print run, or even between different print runs.

CYMK can be monitored using a GMG scanner and the related software. This allows each printing press to be calibrated to produce a standard colour, regardless of each machine’s individual characteristics. This is why commercial printers use CMYK most frequently, as it helps to ensure consistency of colour across print runs and also across machines.

Converting RGB To CMYK

If you’ve designed some artwork in software that produces RGB documents, you may run into some problems when sending this artwork to print. This is because conversion from RGB to CMYK can result in colour variations, as the colours are created differently (remember: additive versus subtractive).

It’s best to use design software that will automatically save and export your document in CMYK settings, if you want to avoid any last-minute problems with colour conversions. If you’re not sure how to do this, check out our step-by-step colour guide to help.


Jennie Talbot

About the Author

Hi! I’m Jennie, and I’m the Creative Lead at instantprint. I love using my design knowledge to inspire small businesses to think outside the box when designing their print.