The guys at Case Modders Australia have pulled out all the stops for this one. This is something everyone will want to read about. Its a quick article on painting fans! Heres a quote:
This method can be applied to all 12v tube-axial fans commonly used in PC's with only a little variation for the different brands, though in effect, it is the same technique. The first thing you need to do is remove the blades of the fan from the mounting.