Sally,
Not Janet here, but am opinionated on the subject :shock: It's easiest to just wind bobbins of your top thread, so you don't have to worry about dots of bobbin color popping up, which it likes to do with blanket stitch, even with lots of tension adjustments. This all depends on how many layers & what kind of stabilizer, how much starch, and so many factors that it's just easiest to have the threads match.