A red may work really well, but just a bit of advice. Do not sew it on until you have auditioned the outer border. Especially if you are limited in your fabric choices using the fabric in your stash - you might change your mind. Usually the quilt will speak to you (I know this sounds nuts) - but when you have the right combination you will know - let it rest overnight and check it again in the morning. There are times I have found a fabric I really loved and thought of an inner border - and - when the inside of the quilt was finished - the fabrics I picked for the inner/or outer just did not work.