The color of any object, including snow, depends on the color of light under which it is observed and the wavelengths of light it absorbs and reflects. The white color of snow is due to air trapped within the crystal formation working with the ice to reflect white sunlight, causing it to appear white to the human eye.
White light contains all the colors of the rainbow, as demonstrated using a prism. Leaves appear green because they reflect green light while absorbing the red and orange colors. Powdery snow absorbs very little light while reflecting most of what hits it, giving it a white appearance. Each tiny snowflake becomes a mirror, reflecting the light that strikes it. As snow packs tighter in glaciers, it absorbs more red light in the mass, and this causes the snow to take on an eerie blue color. The increase in light on a cold, clear night when snow covers the ground demonstrates its highly reflective nature. If snow is observed under red light, it appears red. When pure water forms into ice, the solid takes on a clear nature. However, if water from a sink tap freezes it has a white appearance, in part due to the aerator on the tap, which adds air to the water.