Pink is definitely a color associated with eroticism (frankly everywhere I feel; if not that than at least romance, and red being more "erotic"), but the hair color thing to me is odd too.
I'd primarily associate it with calm and quiet, somewhat bookish characters, like Nodoka (Saki), Miyuki (Lucky Star),Watashi (Jinrui) and so on. Unless it's a very striking pink, then it's more "genki girl" I'd say.
But maybe the confusion is that pink real life hair is seen that way and that it's different in manga and anime? I wouldn't know about that, so that'd make some sort of sense to me.