Since you know the wedding colors (burgandy and silver), wearing a coordinating or complimentary dress would be nice. I wouldn't recommend a dress too like the bridesmaid's, but one that would look nice next to is. I do this so in pictures, I still look good with the background, other girls, etc.

I'm old-fashioned and don't wear all black (funeral-like) or all white (competing with bride) to a wedding. The one exception was when my girl-friend's wedding colors were black and red and wanted us (all her sisters) to wear black. It was really elegant.

What time of day is the December 27th wedding? The time of day will dictate the formality of your outfit.

I would think that a Christmas time wedding is a wonderful time to wear some luscious velvet dress that you want to buy but can't justify! Or, one of those classic organdy plaid skirts.

I'm in the "never wear black or white to a wedding" camp, too, btw.