Bridesmaid Dress Colors

Hi All,
Tia for any and all help you can offer.

Because we had to postpone the wedding twice(thanks to COVID), we found out the original bridesmaid dress color was discontinued by David's. After much discussion, I chose three colors for the dresses(with the intention of two girls wearing each of the colors.) I'm not picky at all with the style or cut of the dress, I just asked the girls to get the color I specifed for each.
After having the colors assigned to the girls, my one bridesmaid text me & said she got another color because the one she was supposed to wear "washed out her complexion" and she didn't look good. While I'm all for having my girls look good, it now puts me in a bind because I have to ask another girl to switch colors...and it's not really fair to everyone else who is going with the flow. Also, I'm worried that more girls will decide last minute to change the color & the ratio of colors won't be even..
Am I overreacting or is it inconsiderate to switch dress colors? I'm not picky at all(don't care about how they do thier hair, or which shoes they choose), but having an even number of colors is important to me for pictures.
Any suggestions on how to politely tell the girls the colors of the dress can't change?