I love the colors, and yes, the dark sashing will make it pop. In the future squares, you might want to try ironing away from the light colors so the seam allowance doesn't show through the white fabric.
I think it will make a lovely quilt. I have a tendency to use too many rich or bright colors-- and then the colors compete with each other; I'm slowly but surely learning to incorporate softer, paler and more neutral colors.
-- jillaine