I'd say "Do whatever colour is your favorite" but I don't think that would help you.
First, I would ask your bridesmaids what colour they would like to wear best (although that may become an argument, so think about that idea)
and from there, if there isn't a colour they can agree on, I would probably do the colour that isn't displayed as much.
For instance, if you had lots of green plants would you want your bridesmaids in green also? or would you rather they be a purple that, brings out the colour of your butterflies?(if their purple)
Or maybe your "soon to be husband" favorite colour is blue?
Just some ideas...