I would also border and sah in green, as that is a color that is common to each block. For added interst, you might use a strip of green, one of white and an other green, thus making 3 strips for each sash. At the intersection of each block sash, you could reverse and do white, green, white, thus creating a sort of 9 block effect. I believe the white helps carry the eye, whereas a solid green sort of stops the eye. I hope this makes sense! What a beautiful find! And isn't it wonderful that you can carry on and finish the handwork this other lady started, that it's not lost!