Use invisable thread , often refered to as monofilament . It comes in clear , and smoke color( for use on dark fabrics , and does not relect the light as much). I use it often to give texture to an area but do not want the quilting to detract or compete with the patchwork design.
If you choose to use , remember to adjust your top tension. Most machines need the top tension to be loosened for this type of thread.