Black. Tell your BMs they can wear any black shoe they would like. Nobody will notice the shoes your BMs wear. Don't make them match, and don't make them buy new shoes.
They can all wear silver shoes... my girls have aqua dresses, and I am letting them all wear whatever silver shoes they want... It goes with most colors.
Ok, I have different color choice: Taupe is very hot now and it is anticipated it will be for a long time. Taupe elongates the leg and goes with any color. If you look at magazines like People or a style mag, it is very popular.
I second going with silver or an accent color (my girls wore purple w/ blue, they also carried purple bouquets). Dont make them match, just give them a color and let them go.
Re: what color shoes with peacock blue dress?