Again, thank you for your opinions. I think it's clear that there's no general consensus on this issue!
I did speak to mil this afternoon. I should probably preface this by saying that she does have form for getting the wrong end of the stick and I thought this might be one of those occasions.
I told her I wanted to speak to her about her dress choice. She told me she had returned the dress. I said "oh perhaps that's for the best. I don't think cream is the right choice." She said she had tried both the blue and pink versions but apparently the jacket is a slightly different style and she doesn't like it.
She then showed me a dress she has bought from Topshop. Very pretty, floaty, cream background but lots of pattern. She declared it too informal for the wedding. She possibly had a fair point.
So after some more discussion she said that she had a cream lace dress in her wardrobe. She would probably end up wearing that!!! (I suspected this would happen - either she doesn't listen to me, doesn't understand what I am saying or deliberately ignores me!!!)
I reiterated that cream was what I had an issue with. I suggested that my feeling was it should be reserved for the bride. She seemed surprised. She clearly does not think it's a problem. I found it a bit awkward having to explain what I consider to be good manners to a woman 30 years older than me! So I did it in an "I'm so daft, I have this silly belief that cream/ivory is only for the bride. And some of my friends even think it's bad form to wear cream. And we wouldn't want anyone to talk would we?"
I think she got the point in the end! Hopefully...
Anyway, other than the minefield that is the mil's dress choice I am totally happy about the wedding and getting married and will surely have a lovely day.