I would really recommend that you use corner stones with your sashing.i think I'd just do them black like your sashing. Without the cornerstones it makes lining up the blocks a little tricky.it can be done but it's much easier just using the corner stones. I made a quilt this summer and didn't use cornerstones. It wasn't easy getting everything aligned. Tried to save time and sort of made a mess of lining up the blocks. What a beautiful and colorful quilt you have created.