For better or worse, I decided to go with the thread that read darker (and as I stitched, a lot more purple than I thought it would) and am varying the size of the bubbles to include some fairly large as well as fairly small ones. Good variety in sizes seems to make this design work best. This picture makes it look like a lot of light is showing in the thread, but in reality, it reads more like occasional highlights. I wish my stitching was more even, my circles more consistently round, but this is my level of free motion quilting, and I just have to be ok with it. So it's been sink or swim, and I think I am staying afloat, or does that hand look like it belongs to a drowning woman waving for help? It's taking longer than I thought it would (am about 2/3rds done) and using up lots of thread. Yes, I'm eyeing the spool of King Tut thread and hoping it lasts.