Ann CAssandra : Bekku

Well I've decided I'm going to do a little cosplay of Bekku from the manga Ann Cassandra.

I decided than since it will be on a blistering summers day, I'm going to stick with half black sleeves instead of a killer all long black/gray sleeves. So This is a basic loook, also, my dress thing is light brown.

I was wondering for anyone out there, can a dress that's cotton and spandex be bleached well? Or will it ruin the cloth? because im planning to make my brown dress white.