Like Yvonne, I wasn't going to comment, but I can't stand it! Throw that invisible thread away!! It's not worth the trouble when it unravels, breaks with use of the quilts, table runners, whatever. I stopped using it years ago, right after it came out and was touted as the "answer." It's the answer to nothing! I hate it, can you tell?
I might suggest that whatever thread you use (that you like) for the top may just be the answer for the tying together of front and back. I often do that when I'm using lighter colors especially on one side or the other.
JMHO,
Sharon