What a pretty cheerful quilt. What if you SID the inside each block then did some ribbon candy around the solid colored sashing then just a wavy line around the outside sashing. Or if you don't want to do all that SID do some kind of motif inside each block. Look at coloring books for ideas for the inside block. I cut from coloring books all the time then enlarge/reduce to the right size for my block and transfer it to a heavy cardstock or poster board. Cut it out then use it to trace with chalk and stitch the motif or object. Good luck. Can't wait to see it when quilted.