I think I would pick one of the dark browns you have in the quilt and try to find a solid brown like it and use a very narrow strip then perhaps some of the blue you have in the quilt in a narrow strip next to the brown. Maybe even use brown like in a tut I saw of Sharon Schambers as a cording like for the binding or in the border, go to her site and check it out. Just type in her name in the search and she has a lot of tuts. I think something plain since there is so much going on in the rest of the quilt. Don't detract from the quilt by using a busy border.