I'm going to be blunt. There's a difference between wearing all-black and being Goth. If you dress like a goth chick: all black, fishnets and platform shoes, black nail polish and over dramatic make-up, people are going to think you're a freak and not someone who fits into any kind of group, least of all a sorority. If you're in the former category where you just gravitate toward black clothes, it's not the same thing.
Yes, there are plenty of girls in sororities who are not blond barbies, but they also fit into some kind of conventional norm-- or managed to pull it off during recruitment!
Enjoy the rest of the week, add some color to the next round of your recruitment wardrobe if you're feeling self-conscious about the all-black, and go into this process to make friends. At the end of the day, if you're a goth chick, you're not going to fit into most of the sorority chapters I have observed. If you're just a lady who's into black clothing, again, that's completely different. My former roommate is in that category-- even her bridesmaids wore black and silver and she wears only black, white and tan!
Something tells me by the recruitment you're having that you are not the "goth chick" type-- put your fears aside-- the week will soon be over and you can get back to the important stuff: worrying about classes and what to wear out on the town!
And maybe shopping for a pink skirt or a blue dress to wear to a sorority meeting. LOL.