Colour tends to be a very subjective subject, because we all perceive colours in different ways. In an effort to communicate clearly, colour models were invented to establish a benchmark. A colour model is simply a standardised method which people have adopted to describe colours.
There are a number of different colour models used to describe colours. The most commonly known is RGB, which stands for Red, Green and Blue. This is the colour model used for televisions, computer monitors or any other screen devices. Another colour model is HSB, which stands for Hue, Saturation and Brightness. This model is often seen in illustration and image editing software. The colour model used for printing is called CMYK, which stands for Cyan, Magenta, Yellow and blacK.
The CMYK model is not called CMYB because B stands for Blue (as in RGB.) K is used, being the last letter of blac(K.) and is also described as ‘key’. For the purposes of printing, we will look at the CMYK colour model in greater detail.
CMYK is called a ‘subtractive’ model because the colours are masked on the background (which is typically white.) For example, if magenta ink were spread on a sheet of white paper, the magenta ink ‘subtracts’ brightness from the white background. So if the absence of colour is white, then black would be the result of a full combination of Cyan, Magenta and Yellow merged together.
Conversely, RGB is an ‘additive’ colour model because red, green and blue light all combined together create white. The absence of any colour results in black. Additive RGB colours (eg. a picture on your computer screen) often appear more vibrant than subtractive CMYK colours (eg. the same picture in a magazine) because RGB colours are made up of light shining through the pixels from the back of the screen.
Cyan, magenta and yellow are the main pigments used in CMYK colour reproduction. While in theory black would be created from a full combination of all three colours, in practice this is not so. Varying degrees of imperfection in the inks generally result in darker colours coming out muddied and indistinct. To correct this problem a black separation (K) is created alongside C, M and Y. Using a dedicated black improves the shadow and contrast of the image being printed. This is why printers often call black (K) the ‘key’ colour.
While the CMYK colour model encompasses millions of different colours, it does not cover the entire spectrum. ‘Spot colours’ are colours which cannot be achieved in the CMYK colour space. Pantones are a widely used range of colour inks which can produce colours CMYK cannot. Quite often one or more Pantone colour plates will be created to print colours alongside the CMYK plates.