My frogs are healthy so I'm not worried or looking for advice, but I'm curious as to whether other people's frogs change colours in the same way as I never see this mentioned anywhere. When my frogs are in a bare-bottom tank, they have spots all over their bellies and the colours on their backs go very dark. When they're on sand, most of the spots on their bellies fade away and their base colour between the patterns on their backs changes to roughly the same colour as the sand substrate that they're on. I've heard people say that certain substrates bring out their frogs' patterns better, but mine completely change colour to match the substrate. Is this common?

Here are a couple of my frogs when they were in a bare-bottom tank:


And here's one of the same frogs on sand substrate:


This is one of my other pairs of frogs. The lighter frog had lived on the sand substrate for a while. I had just added the darker frog from a bare bottom tank:


And this is the same pair of frogs once the darker frog had camouflaged herself against the sand:


At first I thought that the reason that the frogs get spots on their bellies and become darker in bare-bottom tanks was because there was too much light reflecting off the bottom of the tank so they were trying to camouflage themselves. But I've found that they do this even if I never put the tank lights on and even if the tank is crammed full of things that they can hide under. I'd love to know what colour they go on black sand.

Do anyone else's frogs do this?