Blue Is the Rarest Color

Danielle Nadin (Staff Writer)


Color didn’t really matter until some 600 million years ago. The bright hues now used by plants and animals to attract pollinators and prey or to ward off predators were of no concern, because, well… no one had eyes. The diversity of both form and function currently existing within the animal kingdom is breathtaking, from the vibrant plumage of birds like the macaw or the golden pheasant, to the neon scales of the mandarin dragonet (go on, Google it). Color has been an advantageous evolutionary adaptation for all kinds of species.

Most color is produced by pigments, meaning that chemicals produced by the animal or plant reflect certain wavelengths of light and absorb others. Chlorophyll is a well-known example of this. This chemical, located in chloroplasts, absorbs
sunlight, allowing plants to perform photosynthesis, but also reflecting green light and giving plants their distinctive color.

Another type of pigment called carotenoids can essentially be transmitted from one organism to another. Carotenoids are responsible for making berries red and leaves golden in the fall. They are the reason why flamingos turn pink from eating shrimp, goldfinches are such a bright yellow, and you, according to Sara Hallager (a curator at the Smithsonian National Zoo) could turn the whites of your eyes slightly pink from eating too many carrots.

Some color production gets even more complicated than that. Blue is an extremely rare naturally-occurring pigment. For instance, in humans, this eye color is not caused by a pigment at all, but rather by the lack of any pigment whatsoever. How, then, do animals like peacocks and blue jays tint their feathers? Unable to produce or absorb blue pigment, they rely on microscopic structure. The blue morpho butterfly, for example, has reflective chitin scales on the surface of its wings. They bend the light in just the right way to add up wavelengths that correspond to blue in the visible spectrum. If you were to crush up this butterfly’s wings, the residue would be gray, because the structure responsible for their vibrancy would have crumbled.

The same goes for green snakes. They are in fact only capable of producing yellow pigment and creating blue by structural means. When these two colors combine, the reptiles
appear green. When these snakes die, they stop producing yellow pigment and will turn blue. Structurally-created colors last forever, or at least until their complex architecture is destroyed.

Engineers are hard at work trying to determine ways for humans to produce our own structural colors. This would prevent pigments used in paints, cosmetics and textiles from fading over time. If a beetle shell can maintain its metallic blue sheen for 500 million years – as it was discovered in Germany in 1998 – why shouldn’t our paintings, photographs, and illustrations be granted eternal beauty?