What do you use or how do you paint gumpaste, fondant, candy clay/modeling chocolate? Do you use the same technique for all of them? Please help!

Yes, the same technique should work on each one. Use airbrush colors OR thin down gel colors w/alchohl - gin, vodka, Everclear etc.

. . . what are you trying to paint . . . if it is just smaller pieces, you can use luster dusts/petal dust/ or even non toxic chalk . . . sponge eye makeup applicators and/or artists brushes can be used (bflies in my photos were using chalk and eye makeup applicators ) . . . HTH?