Since the early eighteenth century, painters have used the colour wheel, and related diagrams, to predict how colours will mix, to organise them in graduated sequences and contrasting pairs, and to arrange them in harmonious combinations. Artists, along with scientists and philosophers, have also used colour diagrams to set out the relations possible between colours, or the full variety colour can assume. But, although such diagrams are powerful heuristic and logical tools, they embody some significant misconceptions, and create a good deal of confusion, about colour. Drawing on arguments put forward by the philosopher, Wittgenstein, this paper will examine how they fudge or misrepresent the phenomenology, categorisation, and ‘space’ of colour – and the consequences of their doing so for art.