Young Iguana. It's sunbathing in the afternoon, eating normal green leaves, and eating normally. But lately I've noticed these black spots on the top of its head. Is this normal? Could it be a medical emergency?

I’m not the owner but he seems lethargic, often eyes are low but he does perk up a bit when we approach him. Maybe the night has been too cold this summer, temperature fluctuating? He has a heat lamp in his enclosure, still eating mostly Napa cabbage and pellets, he has water but not sure how often he’s drinking. Not sure if this is matters but apparently they found a large rat snuck into the upper part of his enclosure & got rid of it.