First I sew the yellow diamond to the blue diamond from the marked point to the other end of the seam, with the yellow diamonds on top . When you are sewing diamonds together you actually can sew into the seam allowance on the very pointy end of the diamond, because generally this particular join creates kind of an "outie" point, and doesn't require the same folding as an "innie" join. Press open the two diamonds with the bulk on the seam going towards the blue diamond. See photo