Hello,

Darkened skin color is often a reaction to a drop in temperature, not necessarily bad, green tree frogs in the northern part of the range experience cold spells in the wild. Sometimes as weather warms people turn down the house heat, resulting in cooler terrarium temps.

I'd give the frog a more varied diet, try espoecially to include flies and moths; I've written an article on this species which has links toothers on collecting insects, etc.

Good luck and enjoy, Frank