If you are under 40 and more than half of your hair is white, you're "going gray" prematurely. Rarely, this can be a sign of a thyroid or pigment disorder. But most often, you can thank your parents for the early gray genes. Coloring your hair is an easy fix. If you want to embrace your silvery locks, special shampoos can prevent yellowing. Premature gray does not mean you're aging more quickly than normal.