Re: Keeping a male and female together (moved post)
Amity is right, you can pretty much be certain that any Russian hamster that doesn't come from a breeder will be a hybrid (sorry to sound as if I'm splitting hairs here) not a WW hybrid as they are strictly speaking neither WW or Campbells but a Russian hybrid.
Some hybrids do change colour in winter, some change colour to some degree anyway, nothing seasonal they just change as they mature.
I can understand your concern about the males behaviour when alone but it does seem to me that you could be putting other hams at risk for his benefit, maybe different forms of enrichment, scatter feeding etc may have helped, it is hard to say without knowing more about his environment really.
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