Gasp!!! Tinted wax!!! This stuff has been around since the 1940's, and is reintroduced every 10 years or so to hook a new bunch of lazy owners of black cars.
Shoe polish is just as ineffective in restoring "the clarity of an older neglected black finish", and comes in a wide range of colors. If a clear coated paint coat is intact, clean and waxed, covering it with a coating that absorbs light (that's what a filter does) can't improve its appearance.