Wow. I have seen a lot of white's change before, mine and others, but never saw one go that dark brown. If he changed due to stress, his being in that little critter keeper wouldn't be helping it in anyway, so I wouldn't expect him to change back in there. But they need to go somewhere while their tank is cleaned
Did anything change in the tank recently? Humidity? Temps? Decor? Not that any of those necessarily caused it, but it's a good place to start.
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