Yeah, as PW said, they would naturally turn white in winter to blend in with snow.
Most domestic WW won't change colour, but sometimes their coats can lighten to coincide with periods of light. If a hamster has been exposed to only a few hours of light a day, their body's would instinctively respond as to winter photoperiods.
My Todd was almost white when I first got him as in the shop it's quite dim out the back with the hamsters, but his grey has come through now.
This is actually a good way to determine a hybrid. A hybrid with strong WW genes would change colour somewhat, but one with lots of Campbells in it's line may not. Hybridization effects the ability to change colour.