"To answer this, we must first look at what makes us see colour in any object. Why do we see grass as green and the sky as blue? It's complicated, but it has to do with what kind of light gets absorbed by an object, and which light gets reflected back to our eyes. We see grass as green because it reflects back green light, and absorbs everything else. Ice is clear because light passes straight through it, and very little light is reflected. But because snow is made up of tons of snowflakes, there are so many places for the light to reflect that nearly all of it is reflected back. This makes us see snow as white."