It depends-if you like your quilting skills, pick the color of thread that compliments the quilt top and let it show on the back--if not, or you want the piecing to be the focus, select a neutral thread color that will blend in or "disappear". My quilting skills are not the greatest, so for this reason I always select a back with a print and in the same color as the thread I plan to use so the quilting doesn't show up that much on the back.