My son is 19 years old he had a spot the size of a half dollar on his head that went bald. after a few months the hair started growing back, but its real dark. His hair is Blonde.
Patchy spots of hair of a different color may be associated with a genetic predisposition or a mole or can be just normal. He may have had ring worm and the regrowth of the hair came in pigmented differently. You may want to have your son follow up with a dermatologist.