  Of course, as Smart recognised, this leaves the identity theory dependent on a physicalist account of colour . His early account of colour (1961) was too behaviourist, and could not deal, for example, with the reversed spectrum problem, but he later gave a realist and objectivist account (Smart 1975). Armstrong had been realist about colour but Smart worried that if so colour would be a very idiosyncratic and disjunctive concept, of no cosmic importance, of no interest to extraterrestrials (for instance) who had different visual systems. Prompted by Lewis in conversation Smart came to realize that this was no objection to colours being objective properties. 