I have had my whites tree frog, nugget, for a little over a year now and he seems to be doing fine except I just noticed some light-colored discoloration on his back. Does anyone know what this could be? I fear an infection of some kind and I believe I have access to a vet that can see exotics. Please help because I know that he could go downhill fast if there is something wrong

Just so you know the light I use is purple and it reflects on his skin, that's not what I am looking at.