Why is milk white?

Milk is a mixture of water, fat, vitamins, protein, lactose and mineral substances. But what many people don’t know is that milk is actually see-through – in the dark, at least. Milk’s white colouring occurs when the fat that it contains is exposed to light. These fat droplets don’t dissolve in the water component of milk, and they refl ect, rather than absorb, all wavelengths of light. Conversely, if an object absorbs all wavelengths of light visible to humans, it will appear black to us. If the colours are refl ected, we perceive it as white.