We are not only interested in the processes that generate colour variation within populations, but also in what generates the often spectacular colour differences between populations. The frillneck lizard has a large coloured frill, which varies from grey to yellow, orange and red across their range, and is often displayed prominently when threatened by predators and conspecifics. We are looking at the function of the frill, and the role of genetics, environment and behaviour in explaining the geographic variation in frill colour across northern tropical Australia.