BOS or butter oil substitute is a processed vegetable fat product like margarine, so it does not have a milky aroma like real butter which is made from the main ingredient of milk. But usually, BOS products have added aromas that resemble butter or milk. In fact, some manufacturers claim their BOS products are a mixture of vegetable fats and milk.
Unlike margarine, BOS products usually have a more transparent and bright yellow color, some brands even have a pale yellow color similar to the color of real butter. Compared to margarine, BOS has a softer texture similar to butter. However, some BOS brands also have a slightly harder texture than the original butter texture but are still softer than margarine.