That's a good question Rainbow! And a tough one to call. If I were doing it I'd lay some of the black thread across the whole area (along the marked lines) that you're wanting to quilt and see if you can't get some idea what it will look like. You won't have that density of thread of course, but it might give you some idea how it will look when it crosses to the contrasting colors. I like it when my stitches show, so I'd probably just use the black thread. But another option would be to use a muted charcoal gray thread. It's more neutral and might work better on the combined colors. Try that and see how you feel about it. I've taken tops into the store with me and laid the threads across my work to audition them. No one's ever minded my doing that. I don't unwrap much though, just a few inches.