I like using monofilament thread- that is what I used on the oriental quilt I just finished- since the top was ivory, black & deep pink and the back is a natural muslin- I used the invisible thread on top and a cream cotton in the bobbin. size 14 (long arm) needle and loosened the top tension just a tad- worked beautifully- since I was all loaded up with that combination when a customer brought over a new t-shirt quilt to have quilted - with multi colors on the top and a creamy flannel for the back I went ahead & used the same (although with a new needle) worked great on that one too- I was concerned since the t-shirt quilt is so much heavier-with the t-shirts, interfacing, batting and flannel back- but it worked just fine-no additional adjustments were necessary.