Definitely black for the sashing and border. I also would do outline quilting on the edge of each pieced area in black, so it defines the piecing...mainly because the quilter used the background fabric in some of the piecing and it fades out. By doing some outline quilting in black it will define each area clearly. It will be striking in black. I probably would scallop the black borders, too, for a little interest and to soften the quilt.