Space & Innovation

Is the Sky Really Blue? Five Surprising Facts About Color

Did you know there were forbidden colors we can't see? And that the blue you see isn't really blue...

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The way humans perceive color is mind-numbingly complex. The latest study, for example, delves into the mechanism behind how we've come to see in the blue light spectrum, and it involved analyzing 5,040 combinations of amino acids that could have evolved from seven mutations. The overall view, however, is less daunting -- and fascinating. Here are five intriguing discoveries that color our world.

Superhuman Vision Coming to Mere Mortals

"We definitely do not see blue like other animals," Jay Neitz, a professor of vision sciences at the University of Washington, told Discovery News. "We actually use a combination of what people would call blue and green and use both of those for seeing blue." Scientifically, the wave length for peak sensitivity for the human blue cone is 415 nanometers. "If I showed it to you, you'd see it was violet or purple," Neitz said. What we call blue checks in at 480 nanometers -- that's the color used to represent blue in television screens.

Why is the Sky Blue? No, Seriously

Some nocturnal animals usually have UV vision to distinguish shapes and colors better at twilight. As human ancestors gradually became diurnal, our vision evolved into the blue light spectrum. Those early beings still couldn't distinguish between red and green, however, until about 30 million years ago, when they developed "perfect trichromatic color vision," Shozo Yokoyama, a biology professor at Emory University and lead author of the new study, told Discovery News. Even today, 8 percent of males can't distinguish between red and green "because they inherited new mutations from their ancestors that occurred relatively recently (evolutionarily speaking)," Yokoyama said.

Cats Have Super, Psychedelic Vision

That trichromatic vision Yokoyama talked about? It's fairly unique among animals. Almost all other vertebrates have four cones, and others besides primates have two. So dogs, cats, mice, rats and rabbits see mostly greys, blues and yellows. But bees and butterflies can see ultraviolet patterns in colors that we can't see (it's helpful to get pollen out of flowers). Some specific of fish can also see colors beyond violet in the UV spectrum.

Photos: Animal Superpower -- The Eyes Have It

Although some think humans can be trained to see them, most of us don't perceive certain "forbidden colors." Because the frequencies of red and green light and of yellow and blue light cancel each other out, humans don't see them at the same time.

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While our eyes are essential to vision, it's our brain that "really says things," Neitz said. "Our brain interprets the information that comes from our cones." In a 2009 study, Neitz found that monkeys' brains adapted to receiving signals from red cones when they injected a virus that inserted a gene into the monkeys' DNA that randomly infected some of their green-sensitive cone cells. Although their brains were not wired for responding to signals from red cones, they adapted and distinguished between red and green. In the same way, then, humans may develop their own unique sense of color based on our individual experience with the world.

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