Mom’s matching color

So I’ve talked to both mine & my FH’s moms about wearing matching colors for the wedding. I told them they could wear any shade of green or blue but they could choose between the two of them I told them each this a few weeks ago. My FH’s mom just texted me that she bought a dress but it’s purple. I don’t think she would’ve done it on purpose but it does feel sort of weird that she didn’t talk to me about it before getting it. How do I go about this? Or should I just let it slide and not make waves? Maybe it’s too much to ask for them to coordinate outfits?
TIA