Over time, groups of people come to link specific concepts/ideas to certain colours. Sometimes these colour-idea bonds seem to happen almost by decree, for example, when a political party decides to adopt a colour or a colour of a particular thing becomes immediately symbolic (remember when yellow umbrellas were a sign of dissent in Hong Kong?), and other times links build up more naturally and over more time. Not all groups tie the same concepts/ideas to the same colour, so…