Stay blond or back to brunette for a reunion?

I just went blond after being close to my natural color, medium brown, for many years. I am going to a work reunion party in a couple of months; I will be staying with my inlaws. Anyway, I usually do these type of parties in my more natural color hair, but my MIL loves my hair blond, so I am torn what to do the next time I get my hair done. Almost everyone will look fantastic. These people keep themselves looking good, we worked retail, several, including myself, worked in cosmetics.

What say you?