Sherif Afifi just published a new video tutorial dedicated to sewing a two-color endband on one core. It isn't a fast-paced video, so you'll have a chance to see all the details of the process.
Headbanding is the process of strengthening the head of a book. This is done by the sewing a cord onto the backbone behind the boards, which secures the signatures together more firmly. The result is a stronger binding construction, and even the backbone can be prevented from damage.
A good video introduction into creating and sewing headbands can be found in this YouTube playlist.
Well worth a watch before reading the rest of this tutorial. Enjoy!