I'm not particularly a fan of variegated thread. When I've used it before I felt it actually drew more attention to itself then it did hiding. I just did a watery colored quilt with blues, purples, grays with a white background. I quilted it with a soft blue thread. I showed up a bit on the white, which was the effect I was looking for, I was quilting swirlies that would look like water swirling. I think an all over stippling could also give that type of effect of moving water, so I would consider using a soft blue.