Variegated threads are beautiful but do show alot on tops, in my experience, due to the multiple colors. I usually use them when I want my quilting highlighted.
I think a grey, or another neutral, or even an invisible thread, might be your best choice. I also do like some else suggested and pool several feet on top of my project to see what it looks like.
Usually, if I don't want it to show, I also go for a thinner thread, which will hide in the seams better.
Hope this helps. Good luck!