Do you want to feature the colored blocks or the black strips? How big are the colored blocks? If they are small enough to be ok with recommendation from the batting you are using, perhaps let them be as they are with stitch in the ditch between them and then do some sort of design in the long black strips--feathers or one of the template designs that are available. Is there a complimentary "medallion" sort of design that could be used in the corners that would make that look intentional rather than "didn't have enough to miter the corner"? Very nice design that you used in creating this!