No one has answered and I know you are worried waiting. I'm new to chameleons so don't rely on anything I say.
I have just bought a wild caught with lots of black marks on him from injuries during capture, holding or shipping. I am told the black marks will disappear over several sheds.
Another chameleon escaped one day and scratched herself up climbing up a prickly plant. The scratches showed up as black.
If it isn't currently inflamed, I suspect it is an old injury that was under normal-looking skin and only showed up when he shed.