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12/03/2018 Printing FAQs

Explained: The Four Colour Process

Four colours

The four colour process (sometimes referred to as the full colour process or the CMYK process) is a method of printing coloured images. The process owes its origins to Sir Isaac Newton’s investigations into the colour spectrum and modern offset lithographic printers – including two of our own high-volume printing machines – use this technique. Here’s how it works.

Origins of the Four Colour Process 

Sir Isaac Newton gathered together his scientific notes on the colour spectrum in a book called Opticks: Or, A Treatise of the Reflexions, Refractions, Inflections and Colours of Light. He noted that a beam of white light could be separated into its constituent colours and was the first to note down the intuitive observation that some colours can be constructed from combinations of other colours and other (primary) colours cannot.

Additive and Subtractive Colour Systems

Most children learn the distinction between primary and secondary colours in primary school. A more advanced version of this entails making a distinction between additive and subtractive colour systems. Newton’s Opticks describes an additive system of colour that is describing the properties of light. 18 years after the publication of Opticks, the painter and engraver Jacob Christoph Le Blon described a subtractive colour system in his treatise Coloritto: Or, The Harmony of Colour in Painting. In an additive system concerned with the light spectrum, adding all the colours together makes white. In the subtractive system concerned with pigments, adding all the colours together makes black.

Four colours in real life

Cyan, Magenta, Yellow and Key

The four colour process is a subtractive colour system. It uses as its basis the colours Cyan, Magenta, Yellow and Key. The first three colours can be combined to make other colours:

  1. Magenta and Yellow: Red
  2. Cyan and Yellow: Green
  3. Cyan and Magenta: Blue

The fourth colour, Key, is the printers’ term for black ink. An imperfect black can be created by combining cyan, magenta and yellow, but for practical reasons (for instance the creation of fine serifs in black lettering) printers use Key as a fourth colour rather than combining three inks.


By varying the size or spacing of printed dots of colour – a technique known as screening or halftoning – the human visual system will be tricked into seeing a full tonal range. Through variation in the density and combination of our four colours, almost any shade can be reproduced.

Tricky Colours

When we say ‘almost any shade’, it is important to note the ‘almost’ – all colour printing systems have their limitations and CMYK is not perfect. In particular, it has a problem rendering vibrant orange. Fortunately, our sophisticated machines can incorporate a fifth plate. We often use this fifth module to add a clear varnish or lacquer but, if your heart is set on a particular colour that is not available from CMYK, we can add an additional ink.

At Colour Print, we’re the experts on colour. If you have any questions at all about any of our printing processes, please don’t hesitate to get in touch. You can call us on 01603 488001 or email

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