People usually talk about "hot and cold" colours without really thinking of the impact these definitions may have on scientific understanding. These colours are associated with the human sensations of hot and cold, and this idea is consistent with commonsense and daily experience. Interacting with students, we detect conceptual conflicts when they have to interpret phenomena whose origin is the emission of radiation. The contradiction between the scientific explanation for blackbody radiation and their understanding of "hot and cold" colours, reinforced by the coloured images in textbooks, leads frequently to misconceptions and to the remembering of facts and interpretations that are based on context and not on scientific knowledge. In this article we show the difficulties experienced by students with these concepts and make some suggestions of strategies that teachers should use when dealing with them.