Yellow colour of cow milk is due to presence of

Yellow colour of cow milk is due to presence of Carotene.
Milk is an emulsion or colloid of butterfat globules within a water-based fluid that contains dissolved carbohydrates and protein aggregates with minerals.
Cow milk is slightly yellow in comparision with bufflo milk due to the presence of carotene. The fat globules contain some yellow-orange carotene, enough in some breeds (such as Guernsey and Jersey cattle) to impart a golden or "creamy" hue to a glass of milk.