Thanks for all your comments. I removed the crummy stitches and rethreaded with green by pulling the thread thru. I didn't change the tension, but made sure that the thread was correctly seated in the tension disks. Stitched a sample and it was just fine, so it was operator error. I haven't done many quilts with multiple color threads, but I must have just been lucky in the past. From your comments and my bad experience, I can see that I need to check my tension with each color change in the future.
Thanks!!!!!