Even though it's not part of the main trio, I decided to throw in one more hair-related trope for fun before we move on!
Trope: Eerie Pale-Skinned Brunette
Description: Not to be confused with the Brainy Brunette, the Eerie Pale-Skinned Brunette has very dark (maybe even black) hair and never ever sports a tan. Not only is there a stark contrast in her physical appearance that's jarring to the audience, she's got some characteristics that make her a little...odd. While this is a popular description for villains, the Eerie Pale-Skinned Brunette can also be on the side of good. (But if she's fighting for good, she'll do something other than overpower her foes with physical strength. Eerie Pale-Skinned Brunettes are rarely, if ever, portrayed with rippling muscles.)
Examples: River Tam from Firefly, Severus Snape from Harry Potter, a large portion of the roles played by Helena Bonham Carter
Pros: There's something surreal and ethereal about these characters, and they can be depicted as physically attractive. Since they usually have to do something to fit the "eerie" part of the trope, they're most likely not going to be unintelligent. If your work is in the paranormal genre, this is one way to signify that something's up with this character without having to go into a lot of detail right off the bat.
Cons: Waaaaaay overused when it comes to vampires. Way. (Yes, I know, there are reasons, but still....) Also, as a naturally pale person (though I don't have dark hair), I kind of resent the idea that fair skin is "unnatural". (Hey, I never said this feature was going to be unbiased!)
Would/Did I Use It?: Near the beginning of Disintegration, Ro's described as having dark brown hair and very pale skin, leading Callum to assume she hasn't been out in the sun in a while. (True.) He also remarks on more than one occasion how, despite her outspoken nature, parts of her remain a mystery to him. That said, I don't know if I really feel comfortable labeling her with this trope. Enigmatic? Yes, to a point. Eerie? I'm not sure I agree. I wouldn't write this one off for future characters, though.