Depends on how much you want your quilting stitches to show. If the fabric is mostly black, black thread would blend in more, if mostly white, then white thread would blend in more. If you want your quilting stitches to show a little more, contrast the thread. If you want it to really show, stitch in another color entirely, such as red! It would really make a statement!
I have a black and white variegated thread that I have used a couple times in that instance.