Color change too fast??

[DVirginiana]

They get brighter or duller depending on their surroundings. Buried in brown cocofiber, they will tend to be duller. That's one reason breeders take them out and soak them before taking photographs on white paper towels.
I have a WTF that goes from brown to bright green within a few minutes based on whether he's sitting on his tree or sticking to the tank wall.

There can be health things that cause color change (like stress), but it sounds like your frog is fine...