According to colour irrealism, material objects do not have colour; they only appear to have colour. The appeal of this view, prominent among philosophers and scientists alike, stems in large part from the conviction that scientific explanations of colour facts do not ascribe colour to material objects. To explain why objects appear to have colour, for instance, we need only appeal to surface reflectance properties, properties of light, the neurophysiology of observers, etc. Typically attending colour irrealism is the error theory (...) of ordinary colour judgement: ordinary judgements in which colour is ascribed to a material object are, strictly speaking, false. In this paper, I claim that colour irrealists who endorse the error theory cannot explain how we acquire colour concepts (yellow, green, etc.), concepts they must acknowledge we do possess. Our basic colour concepts, I argue, could not be phenomenal concepts that we acquire by attending to the colour properties of our experience. And, I explain, all other plausible explanations render colour concepts such that our ordinary colour judgements involving them are often true. Given the explanatory considerations upon which the irrealist's position is based, this is a severe problem for colour irrealism. (shrink)