Working from a script by Mark Hey-man, Andres Heinz, and John McLaughlin, Aronofsky plays up the thematic parallels between Nina's dissolution and the narrative of "Swan Lake." He dresses Nina in white and her co-players in dark colors, just in case we missed the point.
He blurs the line from the get-go between her reality and her rapidly accelerating fearful fantasies. A split toenail in this movie is never just a split toenail. It's a portal into horror, or, to be more specific, artsy B-movie horror shenanigans.
The technique of visually connecting a crazy person's interior and exterior worlds has been in the movies since at least "The Cabinet of Dr. Caligari" (1920). But Nina has so little psychological substance in "Black Swan," and Portman's performance is so glacéed, that watching her come apart seems like an exercise in voyeurism. Or sadism. It doesn't even matter, on some level, if Nina is a dancer. Her obsession with ballet has very little to do with artistic expression – it's obsession for the sake of obsession (an Aronofsky specialty – see "The Wrestler" and "Pi").