Why does polar bear fur sometimes look yellow or green?

Question from Eve Boyle 

Polar bears often appear white, but it’s all a trick of the light. Their skin is actually black (to better absorb the Sun’s warming rays), and their outer layer of fur is transparent. Under the glare of the Sun the see-through strands scatter light, and they change colour depending on the weather and time of day. Beneath clouds they might look grey, and at sunset pink or red. The clear hairs also change colour when they get dirty; oil from seals can tinge them yellow and algae can make them look green. The organisms actually grow inside the hair shafts, thriving in warm and damp conditions.


Answered by Laura Mears for Brain Dump in How It Works issue 115

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