Mmmm. If I am not mistaken, the watercolor ones have no wax in them and the Premier, etc., do. The wax ones work with gamsol. The different Prisma pencils have different wax contents. I asked on here a while back what pencil everyone used with gamsol, and the replies were overwhelminly the Premier ones.
Here's a link to that thread:
Forums at Splitcoaststampers
Take care and happy coloring!