I just finished a Christmas Fabric table runner (15 minute one) that was mostly red, cream, cream and some purple in color. Prettier than it sounds. I used a new to me variegated thread from King Tut that had only red & green colored thread on the spool and I loved it. It blended in so well both on the backing and top fabric that my 20 year old was amazed. I frequently to most of time use a variegated thread for quilting and like the look that you achieve with the variegated. Believe I'm not a world class quilter but find that the variegated blends in well if you use one that has the the main colors in it.
Chris