My honest opinion is that it's in bad taste and disrespectful to the bride for ANYONE to wear white/cream/champagne at the wedding. Those colors are normally reserved for the bride only to help her stand out from her guests.
If you want to start your relationship with her as you future daughter in law off to a good start, I would suggest you either:
a. Speak with her about it and gage her reaction. If she doesn't like it, then don't do it. If she doesn't care, then you are fine.
b. Find a different color to wear.
