A Colour Alphabet and the Limits of Colour Coding

Paul Green-Armytage


This paper describes a series of studies designed to investigate the possible limits to the number of different colours that can be used in a colour code and the relative merits of colours and shapes for communicating information. The studies took their particular form in response to an observation by Rudolf Arnheim that an alphabet of 26 colours would be unusable. It was found that a text, with letters represented by coloured rectangles, can be read, first with the help of a key and then without. The colour alphabet, tested in competition with other alphabets made up of unfamiliar shapes and faces, was read more quickly than the others. Speed of reading was only matched with an alphabet made up of shapes that were familiar and nameable. Colours are most helpful for quick identification and for clarifying complex information, but where more than 26 distinctions must be made colours must be supplemented by shapes, typically in the form of letters and numbers.

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Journal of the International Colour Association