Milk is 87% water and 13% solid. It contains a number of color-coded molecules, including protein casein, calcium complexes, and fats. Casein is one of the major types of milk proteins that combine with calcium and phosphate to form tiny particles called micelles. When light hits the tiny micelle particles it causes the light to refract and scatter. This causes milk to reflect all light wavelengths and absorb none, making it appear white.
But what if your milk doesn’t look pure white?
Don’t worry, not all milk is completely white in color. Natural cow’s milk is a light yellow color, much like buttermilk than white milk purchased at the store. This is due to the high fat content of natural milk, as well as the lack of homogenization that distributes the fat evenly throughout the milk. This is because milk fat globules can take on a yellow hue due to carotenoids, such as beta-carotene. The beta-carotene levels are higher in milk that is from grass-fed cows versus those who mainly eat hay or grains or the vitamin riboflavin in milk has a greenish yellow color and, the cow’s diet is a factor. Buffalo milk beta- carotene pigment gets converted to colorless Vitamin- A, which makes it less yellowish than cow milk.
If we were to remove some of the fat from the milk (like in skim milk), it would give the milk a different colour because of the wavelengths the light is reflecting back to our eyes. That is why skim milk has a bluish tinge.