So you want a border like on the picture that Kitsie posted? or a border that looks like real piano keys--ebony and ivory.
If it is like the picture that Kitsie posted, it is just lengths of fabric sewn together and then trimmed to whatever width you need. Kind of like making your own striped fabric. Many people use leftover pieces from the body of the quilt. Sometimes the corners are mitered.
If it is supposed to look like a piano keyboard, I would piece a length of black with a length of white and subcut into strips for the ebony and then alternate with white strips for the ivory.