Ah; and the trick that I used, believe it or not, is to Copy viewable and place it under the isolated marbles itself (the viewable is the marbles and background) duplicate that result and set the upper one to color and then run lylejk stencil (thanks again to David for keeping this for me) followed by direction motion blur (I like using 235 degs) and reduce Opacity to taste. I included an XCF for those that want to see a quick example of what I'm talking about.
edit: Oh yea; best to Gausean blur (10 should do it) the lower layer after motion blur; forgot to do this for this example (and am not re-uploading; lol).
edit: arghh; forgot to add the drop shadow using the isolated layer too. Darngat. lol