Why Is Snow White?

Water is clear. Ice is clear. Yet snow is brilliantly white. The difference is structure. A single ice crystal is transparent, but a pile of snow is made of millions of tiny crystals packed loosely together. Each crystal bends and bounces light at its surfaces before passing it along to the next crystal. That bouncing happens at so many angles and interfaces that light of all colors gets scattered equally in every direction. When your eye receives all wavelengths of visible light mixed together, it reads that as white. This is the same reason sea foam looks white, sugar looks white, and crushed glass looks white even though none of those materials start out white. The moment you break a transparent material into countless tiny pieces, it stops transmitting light cleanly and starts scattering it. Deep, compacted snow sometimes looks faintly blue, for the same reason glaciers and deep ice cores do. When light has to travel a very long path through ice before reflecting back, the ice absorbs a tiny amount of red light. What exits is slightly blue-shifted. Fresh fluffy snow scatters almost all the light back before it gets that deep, so you see pure white.