Hybrids can definitely change colour too. I had 2 brothers, one that looked more like an opal winter white but his brother was of argente colouring which confirmed that they were definitely hybrids (as well as their features and behaviour). His brother has changed from his greyish white with a dark stripe down the middle to very white, a bit like yours has. I'm sure the argente coloured hybrid also went lighter at times, too. I can't really tell from that picture if he is a hybrid or not but I think campbells seem to have a stockier build than the winter white though as I have what I believe to be a pure or mostly winter white hamster now and he is so much more dainty and rounded than the other 2 were/are! (He's also much wussier from what I've seen so far but that's just based on one ham..)
Btw stellanova1, your hamster just reminds me of my argentey coloured hamster cookie in his whiter pics! he was such a lovely character, it's nice to see one that looks so much like him
