When I first saw this I thought purple binding. If it is plenty big enough on it's own, I wouldn't use a border however if you need a border I would go with a thin inner border of white and piano keys around like another poster commented. I think large amounts of solid color bordering these blocks would tend to draw attention away from all the piecing work you did on the center unless you could find a just-right patterned fabric with all the colors but that would take away from the scrappiness (is that a word?) of this quilt which I really like. Good Luck!