Is it a daytime or evening wedding? Usually the dress is a bit more formal for evening weddings. But that is not a hard and fast rule.
Really, you can wear most anything - just don't wear white! Don't wear anything that would make you stand out too much. The day belongs to the bride and you don't want to wear anything to upstage her.
That's about the only advice I have. I bet you will have fun!
__________________ Rex & Rowdy's Mom |