1. Get some sugru in a color similar to the tip that you are trying to match.
2. Roll the sugru into a cylinder of the width to match the original. I did not worry about the length of the sugru tube - this will be trimmed off later.
3. insert the antenna into the sugru roll.
4. Wait for the sugru to set.
5. Trim off the excess with a wire stripper or other knife. done! :-)