Nutrients from the cow’s feed, along with water, fill the cow’s udder to make milk. It is the nutrients that give milk its colour. The light reflects off the particles of milk fat, making it appear creamy white. When the milk fat is not there, as in skim milk, the milk has a bluish colour. This is because one of the nutrients, riboflavin (ry-bo-flay-vin), is blue in colour.