To make the block's center unit,
place a Color 2 small square right sides together atop the Color 1
6-1/2" square, with outside edges aligned. On the back of the
top square lightly mark the diagonal. Sew ON this diagonal marking.
Cut off the excess seam allowance. Press the remainder towards the
center. Repeat this with Color 2 squares on the other corners of the
square. Trim to measure 6-1/2" if needed...