I remember reading that when Samuel Jackson heard Lucasfilm were making the prequals, he lobbied George Lucas for a part, he was such a fan of the star wars movies that he was willing to play even the smallest of roles just to be involved in a Star Wars movie , so George created Mace Windu as a member of the Jedi Council, and he was asked which colour lightsaber he wanted and he went for purple (this was at a time where there weren't any particular rules or trends regarding light-sabre colours).