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For most living things the color you see when you look at them is determined by pigments. But some of the most vivid colors we see in nature get their signature looks WiTHOUT colorful molecules. How do these intense colors get their power?

Hosted by: Stefan Chin

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Sources:
Marble Berries:
https://www.pnas.org/content/109/39/15712
https://www.npr.org/2012/09/11/160894364/how-to-get-birds-to-pick-blue-berries-they-can-t-eat
https://www.smithsonianmag.com/science-nature/this-african-fruit-produces-the-worlds-most-intense-natural-color-30070457/
White Chypochilus Beetles:
https://science.sciencemag.org/content/315/5810/348.abstract
https://www.nature.com/articles/srep06075
https://www.osapublishing.org/ao/abstract.cfm?uri=ao-48-17-3243
https://gizmodo.com/new-super-white-material-inspired-by-eerily-white-beetl-1823728796
Black Birds of Paradise:
https://www.nature.com/articles/s41467-017-02088-w
https://cen.acs.org/articles/85/i4/Secret-White-Beetle-Revealed.html
https://www.theatlantic.com/science/archive/2018/01/super-black-is-the-new-black/549869/
General:
https://www.britannica.com/science/coloration-biology#ref391256
https://manoharan.seas.harvard.edu/structural-color
https://www.britannica.com/science/color

Image Sources:
https://commons.wikimedia.org/wiki/File:Seleucidis_melanoleucus_-_20030511.jpg
https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-017-02088-w/MediaObjects/41467_2017_2088_MOESM1_ESM.pdf
https://peerj.com/articles/4621/
https://www.eurekalert.org/multimedia/pub/77703.php?from=274694
https://www.eurekalert.org/multimedia/pub/77704.php?from=274694
https://commons.wikimedia.org/wiki/File:Pollia.jpg
https://commons.wikimedia.org/wiki/File:Black-headed_weaver_(Ploceus_cucullatus_bohndorffi)_male_nest_building.jpg
https://www.videoblocks.com/video/vertical-colorful-light-beams-and-streaks-seamless-motion-background-loop-full-hd-1920x1080-seven-colors-of-light-spectrum-and-rainbow-hktzspn5xj006idsr
Thanks to Brilliant for supporting this episode of SciShow!

Go to Brilliant.org/SciShow to learn more. {♫Intro♫}. The world is filled with an abundance of beautiful natural colors—though, some stand out more than others with super-shimmery blues, whiter than white whites, or darker than dark blacks.

And today, we’re going to talk about three of the most intensely colored living things. What’s really fascinating about these three is that their signature looks are all made without colorful molecules. The color you see when you look at an object or a living thing is determined by the wavelengths of light it reflects back into your eyes.

White light, like the light from the sun, contains all the wavelengths we perceive as colors. And when it hits something, that thing absorbs some wavelengths of light and reflects others. For most living things, what’s reflected is determined by pigments—quote “colorful” chemical compounds that absorb certain wavelengths of light.

Leaves are green, for instance, because they contain chlorophylls—pigments that largely absorb all light except for green wavelengths. And that’s all well and good—for most colors. But the most intense colors we see in nature don’t tend to come from pigments.

They come from a phenomenon called structural coloration. That’s when the light reflected or absorbed depends on the microscopic structure of a surface and not the absorption properties of specific molecules. Take the marble berry, for instance.

It’s the vivid fruit of an African herbaceous plant, and back in 2012, it was heralded as the most intense natural color on the planet. And it’s not hard to see why. These small berries—which are smaller than blueberries—pack a colorful punch.

Their bright iridescent surfaces sparkle and shine in stunning blues and purples. But unlike other berries, marble berries don’t get their color from pigments. Instead, it comes from unique structures in the outer layers of the fruit.

The outermost layer, called the cuticle, is glossy and transparent, allowing light reflected from the tissue below—called the epicarp—to shine through. The cells in that tissue contain translucent cellulose microfibers stacked in miniature spirals. These act like a series of mirrors, reflecting the light back and forth between them.

Depending on the thickness and direction of the spiral as well as the thickness of the cell’s wall, each cell reflects red, green or blue wavelengths. Though most of them reflect blue light, causing the berry to have a somewhat speckled but generally blue appearance. Below these cells is a layer of dense brown tannin pigments, followed by a third layer, an even deeper sheet of thin cells.

The tannins absorb most of the light that gets to them, while the thin cells scatter what’s left to enhance the purity of the color produced by the spirals. In total, the berries reflect 30% of the light that hits them. As for why the berries are such a brilliant blue—well, that’s likely to attract berry-lovers like birds.

In general, plants that make berries are hoping animals will eat them because that means they’ll carry their seeds in their guts for awhile before depositing them in a hopefully-distant location. But marble berries don’t contain lots of yummy flesh, so animals have no particular reason to help the plants disperse their seeds. Except, of course, that the berries are so shiny and blue.

It’s thought the coloration either fools birds into thinking they’re a different, more nutritious species, or simply looks amazing. You see, during courtship, lots of bird species decorate nests or other structures to prove they’re a high quality mate, so a shiny blue berry could bring their mating display to the next level. Either way, the berries get dragged around, helping the plant reach new areas.

While the berries’ 30% reflectance is impressive, it’s nothing compared to the brilliant 70-plus percent reflectance of Southeast Asian Chypochilus beetles. Their whiteness is so bright that it almost hurts to look at them. And they get this super whiteness from their unique scales.

Each is comprised of numerous tiny filaments densely packed together. These fibrils are really good at scattering light, and because the scattering is random, all wavelengths are scattered equally, making the resulting color white. Which is all well and good for the beetles, because it lets them blend in with the white fungi they like to live on.

White things are also useful to us, of course—which is why researchers have created an artificial white substance that mimics the structure of a Cyphochilus scale. This substance is 20 to 30 times more white than normal white filter paper and retains this clarity of color down to a mere 10 microns thick—that’s thinner than a human hair! On the other hand, creating the blackest black requires the exact opposite approach.

Black is the absence of all colors, so to make deep, dark blacks, you need something that absorbs most if not all of the wavelengths beaming at it. And that’s exactly what the feathers of several birds of paradise do. Some people who have sees these birds up close say looking at their feathers is like looking into a dark void.

And that’s actually a pretty apt comparison, because the birds’ feathers reflect a mere 0.05% to 0.31% of the light that hits them. Compare that to normal black bird feathers, which reflect about 3 to 5%. The difference in blackness comes from modifications to small branches of the feathers called barbules.

In most birds, these are relatively flat and thin; all the absorption is done by dark pigments inside the feather. But in the black feathers from birds of paradise, the barbules are curved, dense, and pocked with tiny spikes. These reflect any escaping light back inwards towards the bird, trapping it in the feathers until it’s absorbed.

You might think something that deep and dark was trying to hide, but that’s not what these birds are after. Instead, it’s thought the super-black of their feathers helps them highlight the colors of the rest of their plumage, which they use to during courtship to woo a mate. That’s why nothing but the blackest black would do.

And though there are lots of ways to make beautiful colors, it seems like when nature wants something really intense, light-absorbing compounds just don’t cut it. To understand why structural colors are so much more intense, you have to understand how light behaves. And if it’s been a little while since your last physics class, don’t worry—Brilliant.org has you covered.

Their course on waves and light can give you a more complete understanding of how light behaves, which will help you dig deeper into this kind of material. And it’s just one of their many engaging, interactive courses that teach you science, engineering, computer science and math. And with Brilliant, the learning doesn’t stop there.

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