I use white for all my quilt backgrounds for two reasons:
............I like the crispness it gives to all the other colors
............It's easier to see my pencil markings to quilt
I did one quilt with a grey background because it was an appliqued night scene but it was really hard to see my markings and, when it comes to black, forget it! I can't even use black when I crochet because it's just too hard to see the stitches to determine where I'm at in the pattern!