I hope you decide not to go with sashing. I don't think you always need sashing in a scrappy. Why not add a plain but prominent color border (maybe 2") and then go with an unusual pieced border with lots of white like the center (Maybe 4 or 6 inches wide). Maybe google unusual quilt borders/quilt borders.
I have just finished a Round Robin and think maybe your quilt could benefit from a scrappy border.
Good Luck. Can't wait to see what you decide.