For the black outline to show like it does in the original Yellow Submarine graphic you can't do it via quilting as others have stated. You can try a couple of different things,
Hand embroidered with heavy floss or several strands of floss. I would use a stem stitch or chain stitch.
Make super skinny bias strips (like used in applique) approximately 1/8" and apply that around each shape. You can then stitch down with your machine or fuse in place, or find 1/8 black ribbon to do this with. If stitching, I would probably glue in place first.
Couch black cording or yarn around each shape but you will need a couching foot for you machine. Some people can do it using a regular foot and zig zagging but it is much easier with a couching foot. Again, you could probably glue in place before stitching down.
Paint the black with fabric paint, the kind that leaves a raised up line, using an applicator to get a uniform line of paint. (This would be too scary for me to try personally because there is no room for error)
Once it is embellished you can sandwich and quilt as desired. I think I would be inclined to do wavy lines like water.