Snow is actually water vapor that has frozen in the clouds into shimmering six-sided ice crystals. These ice crystals appear white instead of colorless, as does water, because all the sides of the little ice crystals that make up a snowflake reflect light.
The amazing thing is that although billions of snowflakes fall in a snowstorm, no two have exactly the same design! They vary in size too, depending on the temperature. The colder it is, the smaller the snowflake. In warmer weather, snowflakes have been measured at more than an inch across.
Because tiny, microscopic plants can mix with the snow after it has fallen, places in Greenland and in the Arctic actually have red and green snow on the ground!