The milk is composed mostly of water, but also contains vitamins, minerals, proteins and small fat droplets suspended. The secret of the explosion of colors, is the chemistry: the detergent weakens the chemical bonds that hold proteins and fats in suspension. The fat molecules begin to move in all directions, as that the soap molecules should be of them to join. During these movements, the molecules of food coloring are pushed in all directions, providing us with the opportunity to observe an activity that would otherwise be invisible.