A snowflake is either a single ice crystal or an aggregation of ice crystals which falls through the Earth's atmosphere. They begin as snow crystals which develop when microscopic supercooled cloud droplets freeze. Snowflakes come in a variety of sizes and shapes. Complex shapes emerge as the flake moves through differing temperature and humidity regions, such that individual snowflakes are almost always unique in structure. Snowflakes encapsulated in rime form balls known as graupel. Snowflakes appear white in color despite being made of clear ice. This is due to diffuse reflection of the whole spectrum of light by the small crystal facets.