At my school, there is at least one black girl in each NPC group. The black girl in AOII is one of my best friends in the whole world and we get along so great! (I'm surprised that she hasn't posted to this thread yet because she's a GC freak like me too)
I asked her once why she joined AOII and not an NPHC group and she said that she didn't want to deal with all the bullcrap involved with those groups in order to get in (I have no idea what that "crap" is because I know next-to-nothing about NPHC groups, sadly... apparently recruitment for them is a very secretive and drawn-out process, at least on my campus...). And that she felt that she needed to help AOII get on its feet as a chapter (we were a colony last year).
NPC or NPHC... it's whatever you want it to be, really. I don't think you should have a problem "fitting in" at all. And when you go through recruitment you'll have a good idea of the chapters that like you and the chapters that you like so it'll be easier to see which one is the right fit for you.
Oddly enough, there is one white girl in my school's Zeta chapter... she's so cute and really looks like she belongs there and is wanted by her sisters (she's in ALL their pictures looking like she is having the time of her life.) AND, there is one white guy who's a Sigma at my school. Go figure.

They seem to be very happy.
You'll be happy too, whatever you choose!