Question: Rapid onset of paleness in Tylototriton verrucosus

I have been keeping a couple of juvenile T. verrucosus for a few weeks now (bred in Germany; got them to introduce some fesh blood into my adult group) and over the last few hours one has suddenly paled, turning from a normal dark black-brown to a pale grey colour. The animal is the more aquatic of the two, and both have been eating well since they arrived. Today the tank was was moved across the room and a small water change performed, so they were a little stressed and, having eaten waxworm yesterday as well, refused food. The pale animal seems a little agitated, but that could be down to the water change and change of position. It has not left the water.

Has anyone encountered this before in this species? (I know Cynops orientalis sometimes goes grey, but I believe the transition is slower). I would just leave the animal to settle down and take it from there, but I am leaving for uni tomorrow and want to be sure all is well before I go. All my animals will be in the very capable hands of my brother, but I'd rather not leave him with a sick animal, or without knowing what mught be wrong.

Cheers

Chris