I think it's the black that does the electrogirl thing, everyone in Ladytron and bands like that have black hair, usually short-ish. If it was dyed or bleached out it'd look more ALT ROCK.
Well I'd associate certain hairstyle with certain genres. Devi was the first to do it in this thread, actually. I don't like when people do totally defie such things by whatever though, and I don't think that's what me or Devi was tryig to do. It does annoy me when people talk about getting "Deathrock" hair. It's okay if you see a hairstyle you like, go for it, and it happens to fall under that umbrella. That's what a lot of people who are all "OOH SUBCULTURES ARE THE REAL CONFIRMISTS" don't understand. But unfortuately there are some people out there that they're kind of right about, it's just important not to muddle them up with those of us who realise how useful these things can be as descriptive adjectives, rather than full on definitions.