Actually, when I was planning my wedding a few years ago, it was very "in style" to give the guest a dress code (I was on a wedding forum). Not many couples did it but the ones that did obviously had more money than they knew what do to with and so did their guests, so they had closets full of clothes to go through and if nothing suited, it was an excuse to buy more. These are also the couples that spend $300/plate for the reception.
Do you have a white t-shirt? Black jeans? I would wear that because you are fitting into her color scheme so she shouldn't get mad about it. Nice pair of jeans, black heels, even a nice blouse rather than a t-shirt. Nothing says you have to wear a dress to a wedding.
I think it's unreasonable to say what colors the guests have the wear, but I do know it is done in some places. Honestly, it's her day, and while I think it's ridiculous to ask guests to do that, I would try to work with what you have. It is you BF's friend, and you don't want to cause problems down the road.
Do you have a white t-shirt? Black jeans? I would wear that because you are fitting into her color scheme so she shouldn't get mad about it. Nice pair of jeans, black heels, even a nice blouse rather than a t-shirt. Nothing says you have to wear a dress to a wedding.
I think it's unreasonable to say what colors the guests have the wear, but I do know it is done in some places. Honestly, it's her day, and while I think it's ridiculous to ask guests to do that, I would try to work with what you have. It is you BF's friend, and you don't want to cause problems down the road.