If you want contrast, you need to use a light thread on a med or dark fabric and the reverse, dark thread on a light fabric.
But quilting is not always done in contrasting threads, much of the effect achieved in the quilting is the texture added to piece, not the contrast of color. An example is the quilting done in white on white.. you dont see the thread, just the texture created by the quilting...
Also, for hand quilting, I would not use DMC embroidery floss.. I dont think that it is a strong enough thread for quilting. 50 or 40 wt cotton thread on a spool is better. Or regular hand quilting thread.
A thin thread will tend to become part of the fabric... also adding to the reason you did not see a contrast of color.
My 10 cents worth....