Celia, I would just use a simple sashing maybe 1 in or 1 1/2 then a first border of the same size in the gray. then a wider colorful border that has all the colors that you used, The blocks would float and look like they are spinning.
Me- I'm done with clearing tile in the basement. Toilet is out and 95% of stuff around where it was is done, but my wrist just can't hold the cold chisel while I pound on it any more. So after dinner I'm sewing! I guess I have gotten to sew much more than I expected.