My SIL made everyone wear the most horrid shiny fuschia dresses and matching shoes... but they kind of worked with her dress. She's embarrassed about the whole lot now. HUGE pouffy shoulders... and no way to wear them again.
I had simple floor length black dresses made for my girls. I paid for everything, as they were broke. (And I know everyone has black shoes already!) I've seen them wearing the dresses at other events, one just had hers shortened. So, good choice, I think. They didn't cost much, about 150 bucks each. Which is more than I paid for the wedding dress... but ebay didn't have anything I liked in multiples.
I'd monitor the green idea, meggles. See, I'd go for very very dark, possibly moss-green... which wouldn't work well with a bright emerald or kelly green. Wedding pictures are forever! I guess it depends on the formality level you're looking for, too. My ideas changed a lot when I found out that my Dad wouldn't accept a beach wedding, and that it had to be in the Catholic Cathedral.