I'll be different and suggest auditioning a mixture of solid white and solid black sashing between the blocks, then perhaps apply a black/white print border with scrappy binding.

Dark blue.

It'll stand out with red sashing! It will draw the eye inward to the beautiful colors in the quilt and not detract. Black or navy simply frames the quilt without a statement. Red is a 'power' color! It's beautiful! Want to see it when it's done! :thumbup:

I would probably go black....or a dark blue! :)