Kassaundra, I vote for the black in the blue squares. Maybe you could do a mock-up test with scraps and take a photo before sewing, just to check?
Carol, Grand Illusion had a checkerboard element, too, and people had trouble with it feeling too busy. Had you considered removing the 4-patch from the main block center and using a single square there? I plan to choose very low contrast 4-patches for those spots. I think your quilt is looking lovely.