I only hand quilt, and it is great! I love the look of all cotton hand quilting thread. But, I don't think there are any "rules" anymore. the color of thread you use is up to you. Do you want your stitches to stand out? if so then use a contrasting color. Do you want them to blend into the background? if so, then use close to the same color as the block. It is all up to you1 Just have fun and enjoy it!!