This is Sheba and her 13-year-old son Inuka in their cage in a Singapore Zoo. They're polar bears, and polar bears are white. Except Inuka there is GREEN.
What zookeepers figured out was that they had some sort of algae actually growing in their hair shafts. Not ON their hair shafts -- IN them.
Polar bear fur is not really white to begin with; it's actually clear, but reflects as white. And the follicles are hollow: because dormant air is a great insulator. But when your hair shafts get clogged up with algae, well that's gotta be embarrassing. Y'see these bears are not typically found in a warm, humid climate like Singapore...
So they treated Sheba with bleach, and were able to successfully clear up the problem, and were watching to make sure there were no problems before going ahead to bleach Inuka.