Taffeta is not my thing... plus, it's way too hot for summer. Anyway, I just got a reply from my DIL and she said the bridesmaids' dresses are short, berry color. She said a cocktail dress is fine, too. I am not sure why her mom got a long dress.
I do know that black is sort of OK for weddings now. The beaded dress I have is too big on me; I got it about 2 months before I started cycling (it's 9 years old). So, I feel I have more choice now. I definitely will not be wearing anything that remotely looks like a "mother of the groom" dress; I want to show off my cycling muscles!