Whatever color works for the quilt. I've used polyester embroidery thread, rayon thread, Gutterman poly quilting thread, C & C poly/cotton sewing thread, varigated cotton FMQ thread. I don't change tension settings, needles or anything, just load and go on a 1956 Singer 301. I did have to purchase an embroidery needle to satin stitch with my Elna with thinner threads, but that's not FMQ.