Recent research from Prof Pettigrew – University of Queensland, Australia – has shown that one of the reasons that some cave paintings have apparently retained their colour for so long is that the original pigments in the paint have been replaced by living organisms that are themselves coloured. This makes dating cave paintings difficult and also makes it hard to know what the original paint colours were. The story is reported by the BBC – http://www.bbc.co.uk/news/science-environment-12039203