I have also wound multiple colors on a single bobbin. Used the thread for hand sewing if the color did not matter. I have removed the thread from bobbins before and thrown it away too. I have used the thread from the bobbin to baste quilts. Uses up quite a bit then. I have started to use Elmer's Washable Glue to baste with though so I might not bother to re-use bobbins with a different color.