I am doing the same thing. I have a tan backing and purple on the quilt top. As my stitches are not great due to severe arthritis, I am doing tan in the tan areas and purple and green in those areas. Mine is an applique quilt top. I am keeping this quilt so I am happy with it. I have machine quilted with bobbin colors to match the backing and different colors on the top. I believe the quilt tells us what it wants and I respect that. Since you are the quilter go with your gut feeling!