My MOH wore this dress (style # BY11024) by designer Sophia Tolli. She had it shortened to about knee length and it was beautiful. It comes in about 30 different colors, is a very light weight material, and has a corset back. Very flattering on all figures (from slim to busty to full figured) because of the halter neck and the rouching. Something like this might work for everyone. Just a suggestion though. We had went to the bridal shop to hunt for bm dresses and my MOH tried this one on. It was really over priced at the shop so we just took a picture of the tag with the style number and went home and found it online for half price!
I figure they will all prefer to have a short dresses, but having a long one shortened is definitely a good idea and I hadn't thought of that. My main colour is purple, so if the shades vary between fabrics I think it will work out okay and I'm not set on having and "exact" shade. I've never seen a corset back BM dress, but that would be an excellent option and will have to keep my eyes peeled for one. I agree that rouching is a great feature, I always seem to go for that style myself. The reason I decided to have them choose what they are comfortable in is because my MOH (sister) is fairly tiny and doesn't have much in the bust region, my one BM (sister-in-law) is fairly slim but busty, and my other BM (FI sister) is not slim (but not obese) and very busty, and trying to find a dress that looks good on all might be a problem.