I would use either the gray or the white. I tend to use white a lot no matter what color the pieces are as I use a fast array of them in most quilts. The real question will be what thread color to use when you quilt it together. There I would use wither gray or a totally different color such as red, or teal if you want the quilting design to show. Otherwise there too I'd use gray if you just want the quilting to blend in.
Phyllis
QuiltingGrannie
Quilter's Pantry