Teeth are not naturally white. They are a pearly shade that, as we age, no matter how good your oral hygiene, gradually turns more yellow. You see this first when a baby’s snow-white teeth are replaced by permanent teeth that are, by nature, more yellow in color. As we get older, the outer layer of enamel on the teeth wears down and exposes the dentin layer of the teeth, which is more yellow. Over the years, tartar and wear-and-tear stains appear and can darken the color of teeth.