You've got the dark-haired Black Swan, and then golden-haired Red Dress. Spencer points out that Melissa wore a Black Swan costume to a charity ball last year, which brings the whole thing about Dark Sisters back from Halloween, which completes the story: Alison was sometimes the golden Alison and sometimes the brunette Vivian; Spencer and Melissa are sisters but Spencer and Alison are also quasi-sisters in at least two ways; you've got the Twin story going on; and all this comes back to Swan Lake too -- Odile replacing Odette at the Ball, masks and illusions confusing identities, creepy bad-touch wizards in charge of everything -- and then even Black Swan itself, the story of a girl who was so tired from being perfect that she tried to be everything. Cover the whole board, black and white all at once, innocence and experience, whore and virgin, and ended up knowing God, in the ecstasy of her own death.
I know I bring up the Jungian thing a lot, but it's so relevant here, because the whole reason for the four Types, the Hogwarts Houses, is that you live in the house of your best accomplishment and your life is about stretching out to learn the other things you weren't born doing, until you know everything. But there will always be one corner opposite your House that you can't ever totally get to, because -- this is how I say it, this is not necessarily how a psychologist would say it -- if you ever got the whole thing at once, essentially, you would know the mind of God and would go crazy or die. Which is what I think Black Swan is really about: She finally accomplished being everything at once, and that's when you go to Heaven.
Or for a more realistic example: Spencer is naturally a Ravenclaw -- actually delivered a whole speech about it earlier -- but has spent this season learning to feel (Hufflepuff) and even coming to grips with her shadow intuition, which presents as faulty or scary visions and dreams. She's always the one jumping to odd scary conclusions and pulling the tablecloth down with her, because her intuition can't really be trusted. But through the actions of A, and Alison, and her relationships with the other Liars, and the serious emotional trauma with Toby, she's gotten in touch with her intuition this season in such a dynamic way that Alison finally appeared to her -- which is always the sign that a Liar has accomplished something, think about Hanna's therapy session, how she's the only one Alison has visited twice and the second time was at Hanna's command -- and that she's going to be the one who solves the mystery in a little bit.