Blue: The color that does not exist … in nature.

By Cameron Dowd

Whether it’s the blue skies, the green grass, or the red leaves on a tree in the fall, different colors make up everything we see. If you are like most people, you have a favorite color. So it’s no surprise that animals come in a variety of colors. Whether it’s from their diet or genetics animals get their color from pigments. Different pigments contribute to different colors. Pigments such as melanin is what gives us humans our different skin tones and hair colors. Flamingos are pink from the beta carotene that they ingest.

Yet there is one color that doesn’t get produced from pigments. This color is blue. The color blue is exceptionally rare in nature. Hearing this one might think of the morpho butterfly, a butterfly famous for its bright blue wings, yet the wings are not blue, they are brown. Then why do the wings appear blue? The reason the wings appear to be blue is due to the microscopic scales of the wings that have small groves in them. These groves scatter light and only reflect blue light. This is what gives morpho butterflies that iconic blue color.

It’s the same thing for blue jays. Their wings would also be brown due to them containing melanin but due to small pockets of air and keratin in their wings they also only reflect blue light. In fact, this is the reason all birds that are blue appear to be blue.

Blue poison dart frogs are unique among frogs. Almost all frogs have a layer in their skin that scatters and reflects blue light through the top layer that contains yellow pigments. However the blue poison dart frog lacks these yellow pigments in their skin so when the middle layer scatters light only the color blue is seen.

However, this does not mean that blue pigments do not exist. While the morpho butterfly may not be blue there is a butterfly that did crack the code to being blue. The Obrina Olivewing is one of the few species that has blue pigment. These butterflies produce a pigment called pterobilin. This butterfly is one of the only known land animals to have a blue pigment.

So why are blue pigments so rare? Does nature have a vendetta against the color blue? Possibly, even counting the animals that rely on light scattering to appear blue they still only make up about 1% of the animal kingdom. So why not have a blue pigment instead of relying on light scattering. The reason is it is easier biologically to rely on light scattering to achieve a blue color rather than evolving to have a blue pigment.