If you use a red to match the large red block at the top, as a narrow inner border it will help carry the red to the bottom of the quilt where it is lacking. Audition the fabric by tucking it under the bottom corner of the quilt top so you can visually determine what width the red fabric should be. I would at least triple the outer border to balance the overall look. I'm thinking the dark brown or even a med-dark brown would help frame and calm the action of the inner blocks. If brown is not appealing to you, audition other fabric choices at the corner or along a side to find what suits you.