I would eliminate the green. While it plays nicely with your background if you were piecing, I don't think it is the right choice for an appliqued silouette quilt. If a portion of the silouette lands just right on one of the green circles (which are so tightly spaced it would be impossible not to land on one) it could start playing tricks with your eyes and distort your silouette. I think the black or the gray are your best bets. I would lean towards black just because it will bring the silouette into sharp relief against the patterned background and from a distance will not fade into any of those design elements in the background fabric. Any of your lighter colors would do that and you may lose the impact of the silouette.