Jaba - when I did the math for a 6.5" border - to keep the look the same as the center's corner - the border's corner blocks centers would need to be 3.5" (finished) which would make the side strips and corner stones as well as the piano key strips all 1.5" (finished) - that would be some small piano keys.
But how cool would they look if the piano keys were all reds and creams and then make the corner blocks with blue centers and cornerstones with creams side strips?