Understanding colours

Posted on November 2014 at

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The colour profile of a file or document has a direct impact on how accurately it is reproduced in print. A printing press is usually restricted to the four ink colours of CMYK and your computer screen uses the three light colours of RGB, and matching these two completely different models can be tricky.


CMYK – Cyan, Magenta, Yellow and Key (Black)

The CMYK colour model is also called ‘process colour’ or ‘four-colour’ and refers to the four inks used in standard colour printing: cyan, magenta, yellow, and key (black).

Files with a CMYK profile are considered print-ready, these CMYK files can be separated into the four colours to create four printing plates, and during the print process these colours are layered on top of each other to recreate the final full colour image.

But the spectrum of colours that can be produced in printed CMYK has limitations compared to on-screen RGB and does not always guarantee a perfect representation as the colour models are completely different. Colour profiling and specialist adjustment of images can be used to get the reproduction as close as possible when the image is transferred from screen to paper.

Where specific colours are required for branding or consistency, additional spot colours can be added to the press to make a five-colour or six-colour etc print run. These colours are usually from the Pantone Matching System.

RGB – Red, Green and Blue

In the RGB colour model, red, green, and blue light are added together in various combinations to reproduce a broad spectrum of colours on your computer screen.

The main purpose of the RGB colour model is for the display of images in electronic systems, such as TV and computer screens. Therefore RGB files are best for use on computer screens – powerpoint presentations and internet files etc. Before the electronic age, the RGB colour model already had a solid theory behind it, based in human perception of colours.

Different computers and devices reproduce a given RGB value differently, since the colour elements (such as phosphors or dyes) and their response to the individual R, G, and B levels vary from manufacturer to manufacturer, or even in the same device over time. So an RGB value does not define the same colour across devices without some form of colour management system or screen calibration, and what you see on your screen is not always an accurate representation of colours on another screen, and can be far off the colours of actual print.

Pantone Matching System (PMS)

The Pantone Colour Matching System is a standardised colour reproduction system of swatches, so different manufacturers in different locations can all refer to the Pantone system to make sure the colours they are reproducing match perfectly.

Most of the Pantone system’s 1114 spot colours cannot be simulated with the limited four colours of CMYK, but with 13 base pigments (14 including black) mixed in specified amounts. The Pantone system also allows for many special colours to be produced, such as metallics and fluorescents.

Pantone colours are most commonly used where a solid colour, such as a corporate colour on documents need to be reproduced consistently. The additional colour can also be added as a fifth colour in the printing process. Or more colours can be added on commercial presses that can handle them. Pantone colours are commonly used by signage and promotional item manufacturers to perfectly match brands.