You could use black construction paper........or black friction tape. Both are readily available. Friction tape is available at most hardware stores. Construction paper might be the easier route. Cut a long strip of the proper width and coat its backside with a thin even layer of Elmer's white glue. Wrap around carefully until snug and then work out the end. If you have a number stamp and some silver, white, or black ink, depending on what was used originally, you can re-stamp the numbers, too. I purchased a few number stamps. They come in handy for re-stamping numbers after a chassis is cleaned.
T.