SaltPork

Actually Lebell, the answer to why is snow white lies in snow's messy construction. A beam of white sunlight entering a snow bank is so quickly scattered by a zillion ice crystals and air pockets that most of it comes zinging right back out of the snow bank. No one wavelength is preferentially absorbed or reflected, so snow is essentially the color of the sunlight reflecting off it -- white.


But all snow is not so snow-white.
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Occasionally, walking across white snow, you'll see color flashes, like sparkles from a diamond. In this case, a cold, dry night has probably squeezed the last moisture out of the air and onto the top layer of snowflakes, where it has crystallized in a faceted pattern similar to ... a diamond. These little torture chambers bend and split light into its rainbow of wavelengths the way a prism does.
And then there are glaciers, which often look an eerie blue. Unlike snow, which is mostly air, ice is mostly ice. Without the scattering effect of air bubbles, light can penetrate much deeper into ice. And the deeper it goes, the more photons from the red end of the spectrum it loses along the way. Two meters into the glacier, most of the reds are dead.

The colors in sunlight react differently to each molecule -- ice molecules, dog molecules, apple molecules. In ice, it just happens that some blue wavelengths skate the farthest -- 24 meters -- before they're finally absorbed. And until they're absorbed, they're free to scatter and reflect. Some of them eventually find their way back out of the ice to glow blue at your eyeballs.


Determining where the white -- or the blue -- goes when the snow melts really begs a look at the warm version: water.
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The surface of water reflects very little light (about 7 percent). What happens to the other 93 percent of sunlight depends on where the water trickles. Clean, glacial melt in a stream will transmit light down to the stony stream bed, where some will be reflected and the rest will be absorbed. In a glacial tarn, or lake, tiny bits of glacier garbage (ground-up stone and dust) suspended in the water will impede transmission and color the water. As the water spills into an ocean, it will change color again as it mixes with a new assortment of salts and minerals and little life forms.
Those impurities traditionally are blamed for the color of water, says outspoken meteorology professor Craig Bohren of Penn State. He thinks differently. He says water is naturally a very, very faint shade of blue. All by itself. Without the sky reflecting in it, without blue minerals floating around in it, water, the water you drink, is blue.

"You need meters and meters of the stuff in order to see it," he says. "It's like window glass: You think it's clear. But take a look at it on edge. You'll see green."


With thanks to Discovery.com without which I would have had nothing intelligent to say

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It was like that when I got here....I swear.