And It Works Because ...
We know what you're thinking: Big deal. Bad guys always wear black. It's an easy way for the audience to know they're evil.
Yeah, but ... why? Why would that one color have any emotion connected to it at all, let alone fear and intimidation?
After all, black also makes us more aggressive. Researchers back in the late 80s noticed that hockey teams in black uniforms earned more penalties and generally played a meaner game, and not all by mere coincidence. Teams that switched to black mid season were suddenly visiting the penalty box and calling the ref a dick a lot more often, too.
The answer may go back to our built-in fear of disease and uncleanliness; experiments show that people instinctively connect black not only with evil and immorality, but contamination and sickness (if you noticed a patch of skin or one of your teeth turn black, you wouldn't assume it was a good thing).
By the way, there's no way he could've brushed his teeth with that thing on.
So when people see black, to this day it serves as an instinctual cue to thoughts of death and evil that, at least in Western cultures, motivate feelings of aggression.
And choketastic space magic.