After spending a good bit of time and making painfully slow progress sewing together four 6" x 6" square blocks (including the following three)
to make the 12" square at right, I really wanted to explore making an entire 12" square as one piece. Certainly that could be done, but I wanted to use colors to arrange a central diamond motif at the same time. I used SmothFox's Diagonal Box Stitch Square 6x6 for the pattern for the 6" x 6" squares, which makes stripes as parallel diagonals. I was sure I could modify that to make the diagonal stripes align as if they were four small squares sewn together. It just took a bit of tweaking and playing and cheating.
There's just a bit of spaghetti involved. But you can see at the top left and bottom right that I'm just starting to get diagonal stripes at a right angle to what's in the bottom left corner.