How about using white on the top with the same variegated thread on the back and loosening the tension on your top thread ever so slightly so that any 'bumps' will show up on the back, not the front? It's a compromise, but may be your best solution. You could make a test sandwich of the same fabrics and batting to try it out. Luck!
ETA: Besides, it would be a lot easier to 'color' white bumps on the dark back than dark bumps on the white front.
Last edited by ghostrider; 05-18-2012 at 04:01 AM.