Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world.
This week, we’re answering an email from Tenisha Forde:
“I've heard that blue eyes and blue morpho butterflies aren't actually pigmented blue. Are these statements true? Why is pure blue so rare a color in nature? Is it even rare?
Roses are red, violets are "red-absorbing"
To answer this question properly, you really have to start big and ask, what is a color, really?
Light is broken up into a series of wavelengths, some of which make up the visible light spectrum. When sunlight – which contains all of the different colors on the visible light spectrum – strikes a pigmented object, the pigment absorbs some of those wavelengths and reflects back the colors that you see.
In other words, a blue sweater absorbs all of the colors in the spectrum except for blue.
Kai Kupferschmidt is a science journalist and author of “Blue: In Search of Nature’s Rarest Color.”
“If you talk to a chemist or a physicist, they will not even call it blue,” he said. “They always call it ‘red absorbing’”.
"Out of the blue"
So is blue rare in nature? On the one hand, anybody who has looked up on a clear, sunny day could argue otherwise. But when it comes to finding genuine blue pigment among plants and animals, blue is indeed rather elusive. Sure, there are shades of violet, like blueberries or eggplants, but few items in the grocery store are blue in the way that lemons are yellow, or oranges are orange.
And many of the blue plants you’ll find in the floral section have been dyed.
“If you think about the cut flowers that we all know and like…roses, carnations, orchids, tulips… none of these exist naturally in blue.”
So why is this the case?
The gist is that it’s surprisingly hard for living things to build the sorts of molecules that absorb low-energy light from the lower end of the spectrum and only reflect the blues. There are some plants that do it – like the cornflower – but these blue pigment molecules tend to be bigger, and more complicated for plants to produce.
Nature has a way of balancing adaptations that require more energy to build, so evolution seems to have steered most plants towards easier-to-produce pigments.
Blue in name only
Animals on the other hand almost never make genuine blue pigment.
If you take the blue morpho, for example – a gorgeous, almost fluorescent blue butterfly – and zoom in really close to its body, what you’ll see are little structures that look like Christmas trees.
Instead of absorbing all of the other light frequencies, like a pigment, they reflect blues using a sort of optical illusion.
“So we call that structural colors,” Kupferschmidt says, “because it's really the patterning on the surface of these wings… that manipulates the light physically in a way that only the blue light is reflected. And from most angles, all you see is the blue light.”
That’s what I love most about this subject. Color, or what we perceive to be color, is a blend of science, culture, and even philosophy. You can talk about why something is the color blue, talk about what the color blue symbolizes in a particular society, and even ask…are colors real? That’s not just me being funny, it’s an actual debate that scientists have.
“Because the object, again, the cornflower that I see out there, it looks blue to me, but that's because it absorbs red light. Like, in what sense is that blue?” Kai asked me. “And also it appears blue to me, but an animal that doesn't have the same receptors as us is going to see it in a different color. So is blue real?”
Submit your question about the natural world
If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org. You can also leave a message on our hotline, 1-844-GO-OTTER.Outside/In is a podcast! Subscribe wherever you get yours.
