Why does vitamin D come in dry white tablets, if it is a fat-soluble vitamin?

yes it is fat soluble. it is also stored to some degree by the body.you rarely see a deficiency in this vitamin, as long as you have some exposure to sunlight, along with foods that are fortified with it. {milk and some cereals} there is however a risk of build up if you take large doses of supplement, which could lead to a potential for toxic levels.