That is a lovely sample, Rita, and I am not surprised at all that Ginger has found it! As for the thread to use in the bobbin, I would go back to Cindy Needham's philosophy about SID thread colors, with a twist, though. She uses neutral colors that blend into the ditch for her top thread. If you still want to use invisible thread in the top, then pick a
somewhat neutral 60 wt thread like Bottom Line that you might have that blends nicely with the backing fabric. I just put on a bright piece of green fabric similar to yours three shades of Bottom Line thread (#613 sage, #619 tan and #622 grey) and they all blended very nicely. You'll never see it even if it pokes through the top because it's in the ditch and as long as the neutral color blends into with the backing fabric rather than looking like it sits on top of the fabric, you should be okay.