Polar bear fur is not white, it’s clear.
The coat of fur on an average polar bear is about 1-2 in./2.5 to 5 cm thick. A dense, wooly, insulating layer of underhair is covered by a relatively thin layer of stiff, shiny, guard hairs. Believe it or not, their fur isn’t actually white. If you got up real close to a polar bear and plucked one of his hairs you would see that the polar bear’s coat is made of clear, colorless hairs (and you would probably find out how powerful the bear is). The hairs scatter light, making it appear white (or sometimes yellow, depending upon the angle of the sun). If you were to pull out all of the polar bear’s hairs (which would really be stupid) you would see black skin underneath all that white fur.