Is my waxy monkey tree frog sick?

[TheGreatS]

I've noticed over the past week or so that the back of my waxy monkey tree frog has turned slightly brown or tan. The texture hasn't changed nor are there any bumps. His behavior hasn't changed and he's still eating. I feed him 4-8 crickets every couple of days and I dust them with calcium and vitamin powder once a week. The temp is ~85F and humidity is ~35%. Substrate is eco earth. Source of water is a bowl in the tank. I have a 12 hour light cycle set up. He's the only frog living in his habitat. I have another frog in a different tank and it's fine. I've had my waxy for 2 months.

I don't know where I went wrong I'm scared that it's a bacterial infection.

I'm desperate over here. I'd be greatly appreciative if someone has advice.