Even though Earth is known as a “blue planet”, the color blue is seldom found in living beings. Even the blue whale isn’t exactly blue. The occurrence of carotenoid colors like orange, brown, and red far outweighs blue because there is no naturally occurring blue pigment found in the animal kingdom.
However, there is one organism, the Blue Morpho Butterfly which not only exhibits blue colour but also shows luminosity in such a way that the color seems to change when seen from different angles.
In other words, the blue is spectacularly iridescent.
In fact, the blue morpho uses structural color to get its particular shade of blue. Blue is actually an extremely rare color in nature. These butterflies have scales that overlap, refracting light similar to a prism.
This blue color is not because of any pigment, it is because of the arrangement of the scales on the butterfly’s wings.
When you slice the wing and zoom into these scales, tiny ridges shaped like Christmas trees are found. When light incidents, some of it bounces off the top surface and some of it passes into the layers and reflects off the bottom surface.
For most colors, the light waves reflected from the top and bottom are out of phase, however, for blue light, these waves reflect in sync. This phenomenon gives an iridescent blue color to the wings.
Having mentioned that for many blue-birds and insects, the feathers and the chitin respectively can be blue but they are not iridescent because of their foam-like structure.