Solid black is too harsh, too much of a jolt. I agree with PaperPrincess on the black pin dot for the stop border, and would use the other sashing fabric, the off white print, as the outer border.
Any color in the border is going to detract from the color in the pinwheels and make them less important. You want them to be the focus of your quilt, so let them have all the color. Frame the entire quilt in the same fabrics that you used to frame each block and it will unite the whole thing smoothly.