Well, I started messing around yesterday with chalk pastels, and I figured I'd post 'em.
I'm using brown on 3-Color Dragon uniform pants since my photo skills are weak, and this combination would show up the best.
I'm using Prismacolor Nupastels. These are non-oil based pastels, so they aren't sticky and are washable. They should be available in singles or as sets at any half-way respectable art supply store. They also make pencils that with water disolve into watercolor paint. I'll be experimenting with those later on.
Here's what to look for: