What color do you look best in? That is what I would do. But find out what the other MIL will be wearing. My mom and my youngest sister's MIL wore the same dress to their kid's wedding! My mom looked fabulous and the other lady was just so-so. That might have something to do with her attitude, too. But my mom got hers in Alabama and the MIL got hers in Oregon. How weird is that?