I've seen people with their hair dyed green, but I was under the impression that nobody has naturally green hair. But Rashi says (Tazria 13:37)
שער שחר - מנין אף הירוק והאדום שאינו צהוב? תלמוד לומר ושער. Black hair - how do we know that green or red hair that's not gold [are the same as black]? Because it says "and"
It's pretty clear that ירוק is green, like in modern Hebrew, because it means grass and tree leaves in several places (Bereishit 1:30, Shemot 10:15, ......).
Tzaraat itself is not a natural disease. It would be interesting if a known cure is also a miracle unlike anything that happens naturally. Is that what green hair means? Or does ירוק mean something else? Or are there actually people with naturally green hair?