If you aren't comfortable with your bridesmaids looking so different you can give them a guideline that will help them to pick similar clothes.
Focus on the details of what your Bridesmaid(s) is/are going to wear
Color of Dress:
- You can give each bridesmaid a sample of the color and guidelines that are more detailed for example clothes that are "light pink," "have the colors pink and brown in it," or "it can look like anything as long as it has a Big flower somewhere on the dress."
- You can give them a brand of clothing that makes different dresses with the same fabric and color.
Fabric of Dress: The venue of your wedding might look better with different sort of fabric. For example if it's sunny and outdoors you may want your bridesmaids to wear something light and cute that's cotton. If it's inside and the ambiance is fit for a ball then you can ask them to choose dresses that are silk and more evening gown-like.