Normally, snow looks white. This is because the ice crystals that make up clusters of snow reflect and scatter every color frequency in the visible light spectrum. So when sunlight bounces off a snowbank, all those colors blend together, giving the snow a white appearance.
Or at least, that's what usually happens. Every so often, though, Mother Nature throws us a curveball with a blanket of non-white snow.
Pliny the Elder was a Roman naturalist who lived from 23 to 79 C.E. In one of his books, he wrote about red-tinted snow, which ancient travelers sometimes encountered. His hypothesis was that snow changes color as time goes by — like a rusting piece of iron. "Snow itself," Pliny wrote, "reddens with old age."