Hi Lab55,
I'm thinking since the 2 backgrounds are different, and since the butterflies are all different prints, maybe a batik would be nice for the sashing strips. I would probably take them to a quilt store and audition them with various fabrics till one jumped out at me. (Which is how I came to have such a large stash). And yes, butterflies do like flowers so I might find some delicate prints to alternate solid blocks with these you have made-or for cornerstones.