Weddingbee boards

I have three bridesmaids, my two sisters and my best friend. Originally I was going to have them all just pick their own dress as long as it matched my guidelines: similar style, length and all in the light blue category. Our colors are baby blue and yellow. I figured since all three girls and I all live in different cities, it would just be easiest to allow them a little creative reign with their selection. However, I have recently decided that I really would rather all have the girls wear yellow. I originially picked blue because one of my sisters has red hair and super fair skin and I thought she might have a tougher time pulling off yellow. But I am not a fan of any blue dresses I have come across, but LOVE tons of yellow ones. So I am thinking of changing my mind. Am I allowed to do that? I have already told my BMs to start looking for blue dresses, but none have bough theirs yet and the wedding is not until the end of March, so there is still time.

Would it be okay if I asked them to change to yellow? Or would that seem rude and/or pushy?

Any advice would be great!

Thanks!