I will dress in bright and cheery colors, and so throw my enemies into confusion. My foes will surely give up and abandon their quest if they have no source of comic relief. I will not fly into a rage and kill a messenger who brings me bad news just to illustrate how evil I really am. Good messengers are hard to come by. That way, the citizens will be jaded in case the real thing ever comes along.
Morale is better with a more casual dress-code.
Similarly, outfits made entirely from black leather will be reserved for formal occasions. I will not employ devious schemes that involve the hero's party getting into my inner sanctum before the trap is sprung. I will not turn into a snake. It never helps. I will not grow a goatee.