It's a bit hard to see, but on the left scrap, top to bottom, there is a matching light gray thread, then a blue-violet that I'm using on the prints and the back, then a very light, shiny gray. On the right scrap, there is a muted pinkish-violet. I chose to go with the shiny light gray.
It is a type of thread I've never tried before, Art Studio by Superior. I had a lot of problems balancing the tension at first, but finally got it looking nice top and bottom and finished one row of gray yesterday after loading the quilt.
But when I started up again this morning, I only did half of a row before it started shredding and made a big mess. After I unpicked the stitches back to an acceptable point, I found that the top thread was wrapped several times around the spool holder before hitting the tensioning guides. I wear reading glasses on a neck cord while I'm quilting, and hang them over the touch screen on the front when I'm done. I think the cord must have slipped down to the thread path, and when I grabbed the glasses, brought the thread up with it. Either that, or the pixies were playing with the machine in the night. I rethreaded, and did a couple more rows without incident.