Wrong Bridesmaids Dress

I am getting married in May 2023. We’re doing mismatched dresses in dusty blue/green tones. The women in our wedding (4 bridesmaids, 2 grooms maids) were told to get dresses in mismatched colors and given a photo of the 6 color swatches. I also said that if they found dresses in that scheme from other websites or stores, that would be fine! I don’t care too much about the dresses, just as long as there’s no exact color matches. I just found out that two of the girls, both of the grooms maids, ordered their dresses in the same color. One I am close friends with, and the other is my fiancé’s sister who is known to be a bit rude at times. How do I ask one of them to pick a different color? The one I am closer with has been communicating about her color process and has told me that the other colors REALLY didn’t look good on her coloring. My fiancé’s sister didn’t tell me when she bought her dress but I’ve found out both have already been purchased. His sister also isn’t as pale and has darker hair so the other colors would also look good on her. I wish they had communicated more on the colors they were picking, I feel like a bridezilla asking them to change. Help!