Ask any child what color a polar bear is and s/he will exclaim, “white” with great enthusiasm, but truth be told, their fur is actually transparent and holds no color. It only appears white because it reflects visible light. They’re nearly invisible under infrared photography. Polar bear skin, surprisingly however, is black! To humans and other creatures that see only in visible light, polar bears nearly blend in seamlessly with their snowy environment. However, reindeer have outsmarted the polar bear’s tricky fur by evolving a visual system than can see in ultraviolent light, which means polar bears stand out like a sore thumb against their icy white backdrop.
In zoos you may have noticed that polar bears have almost yellow or green-tinged fur. The yellowing of the fur is due to age and dirt, while the greenish color is from the algae that can grow on polar bear fur in unnaturally warm and humid environments.
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