Going gray

Going gray is a genetic issue, so you're pretty much stuck with whatever you get in that department. Some people start noticing stray grays as early as their 20s while other lucky ducks keep all their color until retirement. Going white seemingly overnight -- this is largely a myth as there's no physical way for the hair on your head to instantly turn from brown/black/red/blonde to white overnight. What can happen, however, is stress-induced hair loss that causes mostly the colored hair to fall out leaving a majority of the white or gray hairs behind (resulting in much whiter looking hair).