Black Hair, Black Heart
It is pretty darn depressing the recurring trend I've noticed of hot female characters with black hair that more often than not are villains rather than heroes. Just as blondes are often portrayed as the sweet, pure, virtuous ones, so too then are the black-haired ladies demonized into monsters. And that's the thing: not only are black-haired female characters usually evil, they're VERY evil, being utterly sadistic, sociopathic fiends who are oftentimes not at all shy about using their good looks to seduce men to get what they want. Many of these ladies also dress in black as well as have it for their hair color.
And so, with all of that out of the way, here is a (sadly long) list of black haired beauties whose only beauty is on the outside. I will also be making a list of female characters who (thankfully) avert this.