What Is CMYK Colour?

What Is CMYK Colour?

If you have ever printed anything with a commercial print service, you are likely to have heard the term CMYK. But what does that stand for, and why is that important? Find out how to define CMYK, why we use this colour process for printing, and how to make sure you use the right colours in your print designs.
Find colours and graphics fascinating? Study graphic design at Blue Sky Graphics and start your way as an industry-standard graphic designer today!

What is CMYK in Printing?

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

In fact, ‘Key’ means black. It is called Key because it is the main colour used to determine the output of the image. Black ink provides depth and shading, while, depending on how they are mixed, the other colours create different colours on the spectrum. Cyan and yellow, for example, create a green when one is overlaid with the other.

The acronym CMYK stands for Cyan, Magenta, Yellow, and Key
The acronym CMYK stands for Cyan, Magenta, Yellow, and Key

What Does ‘Key’ Mean in CMYK?

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

Another argument indicates that ‘Key’ refers to the very old presses that used screw keys back in 1843 to determine the amount of ink needed to achieve the desired end result.


Have you ever printed something on your home or office printer and noticed that the colours look a little bit off? Until you start thinking you are going nuts, do not panic – this will happen if you are using the wrong colour profile.

Your computer screen is working in RGB (Red, Green, Blue) and not CMYK. It might appear like this does not make a difference to the finished result when you design things, but it does!

A colour display that is not configured to screen CMYK will show you different colours to those that could be printed. This is because the RGB range is much, much wider than CMYK, meaning that colours can be produced in this palette that would not be usable in CMYK.
There is a very clear distinction between RGB and CMYK in the way the colours work. RGB is additive, whereas CMYK is subtracting.

CMYK Colour mode

If printers are using a digital printing method, CMYK colours would be used to print on paper. This is a four-colour mode that uses cyan, magenta, yellow and black colours in varying ratios to produce all the colours required to print the images. It is a subtractive operation, which means that each additional specific colour means that more light is lost or absorbed to produce colours. When the first three shades are added together, the result is not pure black, but a very dark brown. The colour K or black is used to totally erase the light from the written image, which is why the eye sees the colour as black.

If printers are using a digital printing method, CMYK colours would be used to print on paper.
If printers are using a digital printing method, CMYK colours would be used to print on paper.

RGB colour Mode

RGB is a colour scheme associated with electronic displays such as CRT, LCD monitors, digital cameras and scanners. It is an additive type of colour mode that combines the primary colours, red, green and blue, in different degrees to create a variety of different colours. When all three colours are combined and shown to their full extent, the result is pure white. The result is black when all three colours are combined to the lowest degree, or value. Software such as photo editing utilise RGB colour mode, since it provides a wide range of colours.

RGB colours are known as additive, which means they are made with light. Additive colours start from black and, as colour is added, turn lighter and lighter until white. The screen you are currently reading shows the colours made of light.

How do CMYK and RGB render differently?

These colours are made differently depending on the amount of white space that is already provided and how much “mixing” of colours is required. In order to get the same hue on all mediums, the colours need to be transformed. Highland Marketing has done a great job of explaining why RGB colours need to be converted when creating something for printing: “The RGB scheme has a wider range of colours than CMYK and can produce colours that are more vivid and vibrant. These colours are beyond the range of CMYK to be reproduced and will appear darker and more dull in print than what is seen on the monitor or display. Because the RGB colour mode has a full range of colours, the documents shown in the CMYK mode will always be displayed precisely on-screen. RGB colours, however, do not necessarily appear on the print as they do on the screen. To print a document or an image accurately, it must be converted from its original RGB format to CMYK. You can do this by using applications such as Adobe Photoshop or Adobe Illustrator.” Consequently, the same art seen on a screen display can not be compatible with that printed in a publication.
Subtractive colours are used in the CMYK model. This is where the background starts from white (like a sheet of paper in a printer) and when more colour is added, it gets darker until it turns black.
They are essentially the opposite of each other – CMYK starts white and turns black, RGB starts black and turns white.

True Black and CMYK

Technically, if you put cyan, magenta and yellow together in similar and significant proportions, it would produce black. However, owing to ink impurities, true black is impossible to replicate – that is why printers include black ink (K) and other colours. CMYK colours appear to be darker than RGB colours because the spectrum is less broad.

If you have 100 per cent of all colours (C 100 per cent, M 100 per cent, Y 100 per cent and K 100 per cent), it is a solid black. Similarly, if all colours are set to 0 per cent, the print will be totally black.

Why Do Printers Use CMYK?

Certain commercial printers are printing in RGB but others (including instant print) are printing only in CMYK. This is because CMYK is easier to standardise, due to the variety of colours available. This means that we will keep all of your print items looking completely consistent across the print run. There are so many minor differences in RGB that it is almost difficult to guarantee the accuracy of the colours over the print run, or even within the various print runs.

You can track CMYK using the GMG scanner and the relevant tools. This allows each printing press to be calibrated in order to create a standard colour, regardless of the particular features of each system. This is why industrial printers use CMYK more often, as it helps to ensure continuity of colour across print runs and across machines.

Another major factor is that when you print on paper, you apply pigmented colours to a white canvas, making it darker – which is why we use subtractive, CMYK colours for printing.