It's a popcorn quilt. DH's grandmother made one for us in red and white. She just sewed the triangles shut then whip-stitched them together. So, the embroidered blanket stitch on yours is a little different. No pattern is needed. I don't think there are any standards. I would just try to match the thread you have as best you can. Is there any discernable pattern in the way the triangles are already stitched together? What/how many colors do you have?