http://www.polarbearsinternational.org/about-polar-bears/essentials/fur-and-skin
[snip] It is not actually whiteit just looks that way. Each hair shaft is pigment-free and transparent with a hollow core that scatters and reflects visible light, much like what happens with ice and snow. Polar bears look whitest when they are clean and in sunlight, especially just after the molt period, which usually begins in spring and is complete by late summer. Before molting, oils from the seals they eat can make them look yellow. [/snip]
Bumpity bump bump!
Big oil seals. It figures.