I've gotten into the habit of doing a quick colour study in Photoshop before starting a new painting. I generally work out a colour scheme using either the Kuler plugin in Photoshop or the colour scheme designer which is very cool, or sometimes I'll even take it from the collage paper I want to use. Here is the one for Ashton's pirates painting which I am keeping in primary colours:

here's how it's looking at the moment: