The full version of this article article originally appeared on Motherboard. Most of us were born and will die a certain color, but octopuses are masters of their hue, changing from transparent to shades of red, pink, purple and blue by stretching and relaxing their skin. If we could unlock their secret and wrap our buildings in octopus skin, then city skylines might shimmer a spectrum of colors and opacities as the sun waxed and waned.
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“Octopus skin can switch from transparent to opaque naturally. Our interest has been to figure out how, and to reproduce the effect in a simple and cost effective way,” Shu Yang, a materials scientist at the University of Pennsylvania, told me.Octopuses evolved their color-changing ability for camouflage. But Yang believes the same trick could revolutionize energy efficiency in buildings, allowing structures to heat up or cool off by altering their transparency according to the ambient temperature and sunlight. That’s the motivation behind Yang’s latest invention: A synthetic skin that, like the octopus, changes both color and opacity when stretched.“If temperatures are low, we’d like buildings that are transparent so they can harness more sunlight,” Yang told me. “But if the sunlight is strong, we’d like those buildings to become opaque or reflective. The octopus offered us a template.”
The secret to octopus skin has to do with the unusual way in which the animals produce color. While most creatures get their color from pigments—molecules that absorb certain wavelengths of light while reflecting others—color can also be built by bending and scattering light within molecular lattices. So-called “structural color” is the basis for some of nature’s most dazzling displays, including iridescent butterfly wings and shimmering peacock feathers. Unlike pigment-based colors, which always reflect the same wavelengths of light, structural colors can be tuned by modifying the nanoscale architecture that creates them.
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Cephalopods are masters of disguise, often harnessing both structural color and pigments to modify their cloak based on the brightness of their environment. Take Japetella heathi, a small octopus that lightens or darkens in a blink to avoid predators. When sunlight streams in from above, it passes through creature’s skin unimpeded, rendering the octopus transparent. When a predator shines a bioluminescent searchlight on them, these animals will stretch out, enlarging pigmented proteins and rendering themselves opaque.
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