All it does is cover the end and ~sort of~ keep you from poking your eye out. It will not impact performance, it's just a cap. Only way you'd have an issue would be if the metal inside the antenna touched something else metallic, in which chase the antenna would be electrically longer and detune it temporarily.
If you are concerned about it, you can get Plasti-Dip at most hardware stores. You can dip the end of the antenna in that and let it dry. You can get Plasti-Dip in different colors, if you want to get creative.