Last week when we were in Berlin at the zoo visiting Knut, we noticed that his fur had a greenish tint, which was from the algae that was in the water of where he was swimming. When I get my zoo pictures transferred from the laptop to my big computer, then I will post a link and you can have a look.
I figured that when the algae season subsides, then the polar bears will be back to their normal color. I did find that to be rather strange, but did ask my husband about it, and he's a scientist, so he was able to answer straighaway.