Thank you! Let me guess...bodypaint for Na'vi? If this is just for the purposes of a photoshoot, I'd say that Mehron or Ben Nye creme or cake makeup will suffice, applied with a sponge.

If this is for a convention and you're looking for it to last fairly flawlessly for hours, then I can't recommend an airbrush kit enough. Airbrush makeup I'd recommend is Temptu (pricey but top quality) or Graftobian. A spritz of barrier/sealing spray before and after the application of any sort of makeup will not only enable the makeup to stay on the skin where it belongs, but it will also protect it from rubbing off. If this is full body work, be prepared to be painting for about 4 hours. Good luck!