I do mostly scrapquilts, so I use all my bobbins of every color. It doesn't matter to me as the sewing threads never show. If I was machine quilting, I would use matching thread and bobbin. In machine embroidery, I try to match my top and bottom threads, as no matter how I set the tension, the bottom thread somehow appears on the top at times. Since I don'tlike to mess with tension, I use the same top and bottom.