First I might ask the question of how large you want it and how many blocks you have. I think many of the ideas are good but would stay away from black to honor the era of the quilt. I think the solids and some 30's repo's would be good. I have made sashing that introduces a blending of colors diagonally across the quilt and I think that would be a good way to have both the yellow and aqua. I would experiment with a double sashing (not cornerstones) with both the solids and the reproduction calico prints. You would get a slight log cabin feel and a secondary pattern that would be subtle enough to blend not overwhelm the butterflies. Good luck and enjoy!!