HELP! I'm worried! My frog changed colors!

So I get home last night and his cage is a bit dry, but there's a little moisture in it. But I take a peek at him, and he's fat and sassy and all happy, but then I realize that he's a darker green! What does this mean?

I think it may have something to do with the humidity, right? His cage dries out fast. I have a mesh screen on the top. How can I keep the humidity in where it needs to be?

Oh, but he's eating well. Is it two to three crickets every day for juveniles, or three to four? They're small, so...