Quote Originally Posted by Pactolus View Post
I'll go out on a limb and say that that's their skin naturally changing color because of stress. I've been green treefrogs that are entirely the color of the blotch in the 2nd pic. Infections do not change color that quickly.

A vet visit would still be appropriate though, because color changes like that are not normal.
I don't think that's what's going on. When they change colour because of stress its usually a full body change to a darker colour.

Anyway, he needs a vet ASAP.
Good luck