What Bugswim says is true. Only they do this to spring a successful ambush on their prey, not hide from predators. Other than humans, polar bears really don't have predators to speak of, and human vision along with our ability to interpret what we see would make his camouflage pretty useless. Orcas (aka Killer whales) have been known to eat polar bears, but this is a very rare occurence indeed and therefore wouldn't be a cause for their camouflage.
