Why water is colorless but ice or snow is white?
Main reason is REFRACTION.
During freezing of water; ice will be
Transparent if the freezing process is slow.
White if the process is fast. It happens mostly.
When water starts freezing quickly, it traps air molecules as bubbles. It means snow or ice will be a mixture of 2 types of medium i.e. water & air. Now, when light passes through the snow it gets refracted at the interface of air-water. The presence of air bubbles inside the frozen ice results in lots of random refraction and finally end up with a mix of all wavelengths, e.g. white light.