probably spider mites.
I've heard that spraying the plant with mildly-soapy water does a good job of killing the mites, but i think it would raise the pH (make it too basic) so it would have to be countered with something acidic (lemon juice/vinegar?)...
I'm trying to solve the same problem, and our spots look almost exactly the same, except mine turned white over a week-long period of not doing anything to get rid of the mites.
EDIT: I just read your last post, and, yeah, I've heard the same thing. I just dont have the time to go out hunting down ladybugs (which are known to eat aphids and, maybe, spider mites)