Correct me if wrong, but I believe the MicroMark figures you're referring to are molded in flesh-colored plastic?
If so, you can just paint the clothing, shoes, etc. Or, for diversity's sake, you can prepaint the figures a different color.
I agree with the priming re metal figures. Priming plastic is a good idea, too, but if you're not trying to create award-winning figures, any of the craft paints mentioned should do well right onto the plastic.
You might wash/rinse/let dry the whole lot before painting just to minimize any molding residuals that would make painting not fun. Think of it as a big' skinny dip'!
KD