I think it needs a little bit of a "zinger" color to liven it up. I was going to suggest a very white white, but do you have that in there already? ....maybe if the zinger color was used as a thin sashing between blocks, which would be a simple way to add it. if you already have a bright white in there, I'd look for a dark fabric (a really dark teal?) for thin sashings, something to provide some contrast.