Almost always I use a different color of thread in the bobbin. Most always I use a 50 or 60 weight thread in the bobbin and a larger thread, frequently 30 or 40 on the surface. I do this so that the quilting will show up and be a part of the total project. I like quilting that contrasts with the pieced pattern. Being willing to use a different color thread in the bobbin opens up so many options.