They can be black, white or red. The protonymphs are white from everything i've read. If you see what looks like a bunch of tiny pepper grains in a waterbowl, it's probably mites.

A big clue is if your ball is soaking a lot, has not eaten a big meal, your temps are fine, and you've got plenty of suitable sercure hiding places.

Provent-A-Mite is still the best produce I've seen for getting rid of them.