Sorority Suits Invited To A Black Tie Wedding For A Sorority Sister - What To Wear?

Invited to a black tie wedding for a sorority sister - what to wear? - sorority suits

Hello to all! Question to you all ... My friend and I a black tie for the wedding of one of my classmates invited. I searched the Internet to see what an appropriate use for this event, and so far I have found that boys must wear a tuxedo and formal wear for girls. Although I am something that will probably have to pay late, my friend and I can not afford it stay hotel, a gift for them, and renting a tuxedo for him (we pay for our own wedding, and in the middle of buying a house, so it is a bit tight). Is it okay if in a black suit? Personally, I do not think a black suit and a suit that looked different ... Any idea will be appreciated ... Thank you!