What Makes Snowflakes White?
A snowflake is, as you are no doubt aware, made of water affected in such a way by the temperature as to change it into a crystal. Water, of course, as you know, is perfectly transparent. In other words, sunlight or other light will pass through water without being reflected. A single snow flake also is partially transparent, i.e., the light will go through it partially, although some of it will be reflected back. When a drop of water is turned into a snowflake crystal, a great many reflecting surfaces are produced, and the whiteness of the snowflake is the result of practically all of the sunlight which strikes it being reflected back, just as a mirror reflects practically all the light or color that is thrown against it. If you turn a green light on the snow, it will reflect the green light in the same way. When the countless snow crystals lie on the ground close together, the ability to reflect the light is increased and so a mass of snow crystals on the ground look even whiter than one single snowflake.