Hi,
I took am in the same dilemma… black with champagne/ivory, gold accent. I was going to add a color as well. The more I thought of it, the thought of various shades of the ivory, gold, and champagne could produce a beautiful, classic look with gorgeous cream/pearl colored flowers. Don't do a red of any sort, unless you want it to come out a little more holiday looking. I'm stuck because I don't want the moms in black and the girls in black too. My dress is a champagne with gold accent, and the moms are both in black. So I'm trying to find a solid color for the girls. I'm thinking about a tone of the champagne/light gold as long as it varied from my dress enough or adding taupe/latte color for their dresses so they don't have black. Then I'm going to accessorize the crap out of everything else with ivory/gold/champagne color. I was thinking about doing like a pink rose color, the black, and the cream but I think it is just not as classy for the look I am going for. Go with your gut and do what you want. So, to wrap this up… my suggestion is if you are primarily sticking with the neutrals, go the neutral route with doing various shades of golds, creams, etc and you'll have a very classic look.