Lovely top. When you are FMQ, there will always be some dots (preferable on the back) because we can NOT match the perfect timing like the machine does. Try dribbling various shade of blue and gray thread and see what looks best. I would not have chosen a dark blue solid when you had so much white in your top. Picking a "busy" print with both blue and white would have been easier. It also depends on how you want to quilt this beautiful top. I myself would ditch the blocks changing thread color to match each block. Then you can either do a background stitching such as stippling or just ditch the sashing. Good Luck and take many breaks when quilting.