As the thread "A few updates to Mumsnet" is full, I thought I would start this as from what I've read it's still causing problems for posters, including me. I've gone back to the classic colours and removed Original Poster and My Posts which has improved matters, but the blue is unbearable on some pages. It may have passed accessibility tests, but this user is still getting bad eye strain from it.
I hope that Mumsnet can do something about it, especially if enough of us are having issues with it.
There was nothing wrong with the original blue!