Besides examples of rare albino animals, it seems animals only have white fur during the winter. Additionally, and not coincidentally, the examples I've found live in the northern latitudes with predicable snow cover and have different colored coats in the summer months. Are there any examples of animals that maintain a white coat of fur year round, or are there simply no environments that such a trait would be beneficial in?
Polar bears (Ursus maritimus) have white fur all year long.
There are probably several other examples. @L.Diago gave sheep as example. There are also all white troglodyte species.