It is Coats 30wt quilting thread. The Janome has never been picky about thread before, and I don't recall ever seeing a hint of color on the other side before. The fabric isn't a loose weave. The blue was a scrap in my scrap bin and I don't know who made it. The red backing is a Cranston fabric I bought years ago, and feels like a fine weave to me. On the front of the quilt, which I didn't show because it looks near perfect, is a variety of fabrics. One is a batik from the quilt store, one is probably another Cranston or David's - I remember buying it at Walmart. One is a Kona solid. One is a Moda. The stitches look the same on all of them.
I hadn't planned on washing this when I was finished, but now I'm curious to see if helps.