how animals hacked the rainbow

turns out that there is a problem with green and blue: from a lot of animals blue is not created by pigment, it is a structural color

“The butterflies have a 6-inch wingspan — one side a dull brown and the other a vibrant, reflective blue. The butterflies have tiny transparent structures on the surface of their wings that bounce light in just the right way to make them appear a vibrant blue that’s so bright it almost hurts your eyes. But if you grind up the wings, the dust — robbed of its reflective prism structures — would just look gray or brown.”

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