I start with a full bobbin in the bobbin. All the partial bobbins I use for my top thread. Several weeks ago I had dozens of partial bobbins and used them for piecing a quilt. The color doesn't matter when you make a scrappy quilt. When I think I am getting low on the bobbin, I remove it and then finish using it in the top. You would be surprised on how many empy bobbins I now have.