Hi,
I'm not an expert, so hopefully someone else will confirm, but I don't think those are dumpy tree frogs. Their skin looks rough/bumpy like a gray tree frog's.
Edit: If you were to tell me these frogs were captured in my area, I'd call them gray tree frogs even without a clearer picture, but we only have 10 species of frogs around here, so there may be something I'm missing that would identify them as something else. Them being gray tree frogs would explain the color change. They change color according to the background. I've never seen a really dark shade of brown, but they can change between gray, brown and green... useful colors to hide in a tree.