Hmmmm, that's a tough one isn't it? Usually I would window a light appliqué over a dark background and cut away the bottom layer. Is it a simple shape that you could sew 2 of the shape, stitch the edge and turn right side out? That would give you 2 layers of the shape ready to stitch down. A white on white fabric might be dense enough that the red may not show? I think fusing two layers may give a stiff appliqué unless you use something like Misty fuse. Maybe someone else will have a brilliant solution for you.