Dark Green Frog

[MichielB]

I'm not sure this shows any emotion

Personally, I agree. Although in some animals a discolouration could be caused by aggression.

I've abandoned all my previous ideas about what causes color change- though sometimes it can be in response to cold or darkness, most of the time it seems completely random.

Sometimes I have no explanation for a colour change, with the WTF's I've worked with at work it happened during cleaning the tank (and thus removing the frogs) or watering the plants (increasing the humidity). I've got no specific experience with Red-eyes either.

[jasonm96]

In my experience change in colour has been from stress. Could be temps aren't warm enough too; if they turn a darker colour they could absorb heat more effectively.