Why is snow white? Because snowflakes is frozen water, there is a tiny hexagonal ice, and ice is transparent.
Properly, the ice is transparent. This means that it transmits all of the light rays. Each snowflake itself too transparent!
But snowflakes fall to the ground and lie in the snow randomly. All this loose mass does not transmit light, he can't through it to break. Every ray of light, falling on the top layer of snow, is refracted in a huge number of ice crystals - snowflakes. As a result, all the crystals-snowflakes "pass the light" until such time as it all not "get back", that is, the snow reflects light. And when all the light is reflected from the subject, we find this item in white.
If to be more precise, snow white because white is the light of the Sun, which it reflects. If the rays of the Sun were yellow and red, and the snow would be yellow or red. At sunset or sunrise, when the sun seems to us as pink, snow becomes too pink.