First, talk to each bridesmaid in private and ask what she wants to spend on a dress. Then decide on a budget that everyone can afford.
If you're buying the dresses for the ladies, then the budget is up to you.
Go with your Maid of Honor to a department store and look at the dresses on the racks. Only look at dresses within the budget.
You could go with pink dresses, or a deep purple, or a neutral color like black, silver, gold, mink or latte or tan or other shades of brown, or cherry red. Even white if you want to do that. Or maybe a patterned dress like polka dots, chevron, houndstooth, etc.
Some department stores such as Nordstrom have personal shoppers who will help you for free. Take along a photo of your flowers, tell the shopper what budget your bridesmaids are working with, and she will help you.