I don't think this matters at all. For the most part I don't think they'd ever even be next to each other in photos? Ours were because of a traditional part of our ceremony but they wore navy and dark purple. Our colours were black silver and gold so 🤷🏻♀️.
I think it’ll looks nice wearing something that match your theme colour. However, my mother refused to wear the dress my sister got for her matching with her mother in law. It was a long plum dress. My sister mother in law wore it but not my mother. She said it was too long for her. So my sister ended up buying her a new short dress for my mother cream or ivory colour.
My mom wore pink while my MIL wore blue. Our bridal party is silver/grey. I think they should be able to wear whatever they want. Moms are typically not associated with the bridal party in the same way and they will have their own style they prefer.
I think typically they coordinate with the wedding colours? I'm not 100% sure though. Our wedding colours are silver/grey and blush. My mom will be wearing grey/silver and my Fiancés mom is planning on wearing some shade of pink