Most people use spray paint. But buying the color mask you want from the start will probably be the most durable.
Here's a thread with alot of discussion showing how to paint a mask: http://www.pbnation.com/showthread.p...light=painting
Gonna close this for now as this discussion should be happening in the Masks Discussion forum.
If you tackle this project, post a pic into the Masks Forum and let us know how it turned out!