I'd do the backgrounds in different colors to mimic the skies around trees, in different parts of the day: lighter yellow, blue sky background, a light grey (get lots of those days here in Oregon!), if you could find 'rainy' background, and I'd do one with a night sky and stars, too, if possible. I love the various colors, I'd do every block like that. I'd do a sashing, though, to separate each of the blocks. Do the blocks first and then audition the sashing colors - that's a decision best made after all the blocks are done. Love your block and can't wait to see what you do with it!