I'm not a big fan of alternating blocks. Depending on the fabric, a 9" sq can overwhelm a 9" pieced block, especially when all your pieced blocks are different. I prefer to make an alternating block. In this case, a 6" center sq with a
1 1/2" framing on all four sides (or a 5" sq with 2" framing). The framing then acts as a sashing for your pieced blocks. The center square could be the same fabric in every block or a variety of fabrics that coordinate with your pieced blocks. I would then use a medium to dark color for the framing of the squares.