AITA for wearing a "standard" wedding dress?

My sister (24F) is getting married in a month and I (19M) agreed to be one of her bridesmen. When we were discussing my attire, she told me to wear a nice pair of pants, a white button down, with no tie. She said the groomsmen and groom would be wearing the same attire minus the white shirt, they'd be wearing black. I thought it was a little unusual for a male to wear a white shirt at a wedding, but I'm not really a wedding expert. However, I'm glad she told me what to wear because my first thought was to wear a tux. My sister would have looked like a fool.<br><br>I also tried to get some advice from my mom, who said I should wear a tux or at least a suit. I disagreed and said that's what the groomsmen and groom would be wearing and that I'd look stupid wearing the same outfit. My mom thought my points were valid and said I should just do whatever my sister wanted.<br><br>Fast forward to a week before the wedding and my sister was finalizing all the details for her big day. She asked me what I had found to wear for the wedding, and I told her that I had found an awesome tux that would look great. I showed her a picture of it and she told me it was perfect. I said the tux was a little too big, so I would have to get it altered professionally. She offered to pay for it, saying that she thought a black tux would look better and people might think I was part of the groom's party if I wore white.<br><br>On the day of the wedding, everything was going great. All of the bridesmaids looked great and I got many compliments on my outfit. We took a lot of photos and the ceremony started shortly after. Everything went smoothly and we were all at the reception eating and having a great time. That is, until the groom walked in wearing a white wedding dress.<br><br>My jaw dropped when I saw him walking towards us and my sister was beaming with pride. Everyone else at the table kind of snickered, but didn't say anything. I was expecting all hell to break loose, but it didn't really come until we took more photos. Even though the bride and groom didn't leave the reception, the photoshoot was pretty standard with the wedding party and bride/groom taking photos in the photo booth.<br><br>Things kind of came to a head when we were all in the photo booth. The groom kept making jokes about how good he looked in his dress and how jealous everyone else was of his attire. He then started making passive aggressive comments towards me about how good I looked in my attire, too. I was pretty pissed, but I kept my cool. My sister started scolding her soon-to-be husband and I excused myself for a bit.<br><br>I went and talked to my mom about what was going on and she was upset too. We both agreed that I should ignore the groom's comments and not let him get to me. I went back to the reception and the rest of the night was peaceful. I didn't get anymore comments or weird looks. Everything went perfectly and all of the wedding crashers had a great time.<br><br>I thought everything was resolved, until my sister started sending me angry texts earlier today. She said I betrayed her and ruined her wedding by wearing a black tux. I told her I was just trying to blend in and that she originally told me to wear white, but I thought that was tacky, so I went with black. She said I was being a jackass and that all of the pictures are ruined because I look like I'm part of the groom's party. I tried explaining that she changed her mind and told me to buy a tux, but she wouldn't listen.<br><br>Now I'm starting to feel really bad and I regret wearing the tux. Did I really mess up that bad? AITA?<br><br>EDIT: <br><br>(1) I am not the groom. My sister is the bride.<br><br>(2) I am a guy. I am not the groom. I am the bride's brother.<br><br>(3) Yes, the groom wore a Wedding Dress. Not a Tuxedo or a Kilt. Not even a dress suit. A Wedding Dress. I didn't care that he wore a dress. He could've worn a damn chicken suit if he wanted. My issue was that HE WAS WEARING A WHITE WEDDING DRESS! I had been told since I was five that it was tacky and rude for a male to wear white to a wedding because it would make the bride look bad. <br><br>(4) I agreed to be a part of the wedding party prior to my sister's decision to marry this guy. I agreed to be one of her bridesmen and thought I would just be wearing a tux like every other guy at the wedding. I didn't even know she was dating this guy when I agreed to be in her wedding.