Colour coding
Using colours as signals to sort, label or warn, as in traffic lights, wires and maps.
Also: colour code
Colour coding gives each colour a meaning within a system. Traffic lights, electrical wires, pipes in factories, hospital waste bins, metro lines and school exercise books are familiar examples. It works because colour is noticed faster than words. It has limits. People can reliably tell apart only a small number of colours at a glance, the meanings are not the same everywhere, and some users are colour blind. Good systems therefore add a second cue, such as position, shape or a label, as traffic lights do with their fixed order.