In the middle ages it was a popular technique of the nobility to use arsenic to eliminate the competition.
But, they discovered that if a small amount of arsenic were eaten every day, they could build up their bodies' tolerance. A side effect of arsenic is that the hair turns white. Consequently, anyone who was of the nobility had white hair, which nicely distinguished them from ordinary people.
Eventually, because it was no longer effective, arsenic lost its attractiveness as a noble means of doing in the competition. And of, course, their hair returned to its natural color. By that time, white hair was a tradition for the nobility. That is why the modern judges of the English courts, and other members of the nobility, wear white wigs during formal proceedings. It is the distinctive feature of a member of the peerage.