Non-linguistic colour coding is used to convey information necessary for daily living. Certain colours are associated with signals or messages which are widely understood. Red is generally associated with stop, danger or hazard, yellow with warning or caution and green with safety or go. Blue is often associated with mandatory instructions (Vingrys & Cole 1988). Important colour codes are agreed and standardised internationally (Cole & Macdonald 1988). 

Colour-coding systems can be connotative or denotative. Connotative codes, such as those used in the electrical and electronic industries, provide specific information through colour recognition alone. Denotative colour codes, such as those used on route maps and signage, use colour redundantly as the information is relayed by additional means, such as shape, text and position (Birch 2001). One advantage of the use of denotative colour coding is that it can improve response times and reduce error rates when obtaining information (Smith 1999).