The blocks are all paired -- for every block that has a square in Fabric A and a center in Fabric B, there is another one where the square is Fabric B and the center is Fabric A. The pairs couldn't be in the same row or column, and I might have had some other rules too. Since it's 7 x 9 blocks, there is one block that stands alone. I did something different with that one -- maybe signed it? I don't remember for sure.