How It Works – The Four Colour Process

Like most media today, full colour printing is actually a trick played on the brain and the eye. A full colour image is in fact made up of only four primary process colours: cyan, magenta, yellow and Keyline black  – often abbreviated to CMYK.

Four colour printing is an illusion based on the mixture of the four process colours in a calculated and regimented way, which from a distance appear to produce a larger range of colours and thus a full colour image.

The full colour image is printed in a pattern of dots reminiscent of a rosette shape. These dots vary in size to give the illusion of light and dark, depending on what is being printed on specific areas of the image. Halftones can be easily seen when looking closely at a black and white newspaper picture, with dark shadow areas having larger black dots, and the light ‘highlight’ areas having smaller black dots.

In order to achieve the illusion of full colour, the dots of the four process colours are mixed in the halftone fashion laying each colour dots over the previous, with different mixtures of each coloured dot helping to achieve the desired colour outcome.

For the majority of printing carried out, the use of the four process colours is sufficient. However, it can have its limitations as only around 60% of all visible colours are achievable through it and therefore exact colour matches can sometimes be hard to reproduce.

Bright oranges are one such colour which are impossible to produce vividly out of four colour process and appear quite brown, as you can see below.

Therefore, in order to achieve some colours, special ink mixes have to be used, often referred to as Pantone, spot or PMS colours.


In addition to orange, other colours which sometimes do not reproduce accurately through four colour process are greens purples and blues.

These days, most print work is done is full colour/four colour process, but in summary, if you need a print job to reproduce to an exact colour, for example your corporate colour, then pantone is the way forward for you as the colour is guaranteed to print as expected.

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