The mutations that cause albinism, leucism, and other similar conditions can occur in humans, birds, fish, reptiles, insects...pretty much any creature that possesses color pigments. Many of our domestic animals, such as rabbits, chickens, and laboratory rats and mice, have been deliberately bred to produce white animals.
Several years ago I raised a litter of orphaned opossums with one leucistic baby, who stayed with me as an educational opossum:
For some animals, like polar bears, snowy owls, and mountain goats, having white fur or feathers is a survival advantage, not a liability, allowing them to adapt and survive in cold and snowy climates. A few, such as the Arctic fox and snowshoe hare, can even shed their fur and change from brown to white as the seasons change!
Check out this website if you'd like to see more photos of these fascinating "Ghosts of Nature"