Could be....lol Do frogs get green bruises?!?!?!

From the picture it doesn't look like the skin is broken,inflamed or blistered....as it would be from a burn. It just looks discolored.
Could just be the skin changing color....or adapting to temp, maybe from the lamp as well. One of the froggie experts here would need to take a look.

I'm glad to hear that he is acting normally and it does not appear to bother him. He may just be fine.

~Lesley