Karli-Rae,
Tempura is the paint they used for all of the banners in high school. Water-based, not real durable, and the colors fade quickly.
The powder paint jeffro mentions requires heat to set, and may not work well with non-metallic fly tying type stuff.
Acrylic and enamel are both good choices, as is nail polish. Just test them on a scrap piece of foam, if you want to use it on foam popper bodies. I know nail polish will melt polystyrene plastics. (Don't ask)

Good luck.

Kirk