My son-in-law's Mom got her dress first, however ... that was because her siblings wanted to make darned sure she bought something flattering and not matronly.
That actually helped me. In the beginning, I had no idea, then I at least had one style and one colour that were off limits.

See...that is what I don't understand. As long as the dress isn't the exact same, I don't see why a certain color or style should be off limits.

I always thought that the entire point, was to coordinate with the wedding theme/color scheme/style.

If the wedding colors are say, pink and silver, then normally the flowers, decor, corsages, dresses, and everything else are chosen to match that decor. What is wrong with the mothers of the bride both wearing pink or silver, as long as it isn't the same gown? If one mother wore pink, the other shouldn't have to wear something that doesn't coordinate (like blue or tan) just because the other mother bought a pink dress...

In our case, my DD just didn't want us in the same colour. Complimentary to the scheme, yes but not matching Moms.

The bridesmaids were light sage. As I recall, that was the only colour DD didn't want us to wear.

My DD was pretty much the director or her own show. We just did what she told us The princess doncha know.
And that is probably the trend. It's the brides show and she can dictate whatever colour scheme she wishes.

At our wedding...we had 3 mothers to deal with...to tell you the truth I only remember what my MIL wore because she made such a big deal about the fact that her dress was so much like mine. I had a good mine to make her get a new dress just for that. In the end...I wanted them to be happy with what they were wearing. They were each good enough to ask what our colors were and quite honestly I did not want or need another thing to have to coordinate. Some brides want everything to be matchy-matchy and that is fine for them...but in the end...what really matters?