Colour is not one single kind of "thing." Here I propose a way of categorizing the different kinds of thing that colours are variously understood to be. I further propose that the means used to identify a colour determine what kind of thing it is that is being identified. My proposed categories are conventional colour, substance colour, formula colour, spectral profile colour, psychophysical colour, inherent colour, and perceived colour. I show how these different kinds of colour are the concern of people working in different disciplines and that these different disciplines all contribute knowledge that can be of value in colour design. I also show how recognition of the different kinds of colour can help designers to a clearer understanding of concepts that they use in their own discipline. (C) 2006 Wiley Periodicals, Inc.