How about putting a black thin border around each block against the white background. Just using a black or white background could kind of depend upon who the quilt is being made for.
Of your two photos I prefer the black, but a steel grey would be better yet. The grey would pull some lovely colors out of your blocks and pull the whole quilt together.
Both give a totally different look. The white gives it a softer look and the black makes it all very bright. You need to decide where you are using it and what pleases your own eyes.