I used safe cut scratch remover (lipstick type) and polish on very dark grey metalic quite successfully and was pleased with the result. One day I ran out of car shampoo and decided to use washing up liquid instead, with the result that it lifted off all the polish that I had spent ages putting on, thus restoring all my original scratches! Have since found traffic film remover (truck wash) has a similar effect.
Good luck...
Jimbo, December 2004