Have you thought about a THIN (1 " finished) strip defining (sashing) each of your blocks? Black would work really well. Just enough dark to separate (pop) your blocks but not interfere with that GREAT look you have achieved. If size is an issue you could always add a border or 2 of what else? Scraps !!! to go along with your blocks. That way you stay in the same "family" and aren't creating anything new for the eye to go to.... IMHO I always like black as a STOP! for my eye! Gonna be great whatever you decide. be sure to post when finished, Happy Scrapping.......