Actually, raw milk has an ivory / yellow tint (depending how much grass the cows have eaten vs hay). Grain and soy feeding tends to produce white milk however.

Holding up a glass of grass fed cow milk to store bought milk really shows the difference. The store bought milk suddenly looks bleached white, like liquid paper.

Milk is white, only skim milk is blue, so they sometimes add titanium dioxide as color, but it has to be listed on the ingredients.