It happens before you know it—one day you look in the mirror and realize that your teeth are a yucky, dingy yellow color. Teeth can stop looking white for many reasons, some of them out of your control, such as heredity and aging.You can try various methods for making your teeth nice and white, but there are also some things you can do to avoid getting yellow and stained teeth in the first place. Of course it helps to practice good dental hygiene, but you can also keep your teeth white just by avoiding certain foods.