Oxides/Ultramarines: best for cold or hot process soap -- inexpensive, stable colors 
Micas: best for melt and pour soap, lotions, and bath bombs -- bright, pastel colors 
Cosmetic Clays: good for facial masks, cold/hot process, melt & pour, or liquid soaps -- provide skin benefits and subtle, earth-toned color
Glitters: best for clear melt and pour soap or liquid soap, or for sprinkling on top of a product 
Natural Colorants: spices and other natural pigments to help keep your product as natural as possible