I would go for a medium sized black, then a tiny bright border and finish with a medium black. That would encase your work and not take away from your design, but add a tiny spark of color in the border.
I have seen women sew all the colors together uniformly to make a long line of multi-colored strips which is used as the border strip. I am not sure I explained it right, but I am pretty sure that you know what I mean. right?
I know whatever you do will be beautiful. I hope you are going to show the results later when it is finished.