A friend of mine has had to get a ford door changed and some dents removed and resprayed under the insurance, and when he got it back the respray feathered edges stand out like a sore thumb as the flecks are lighter in colour than the old paint. Its gone back but this is not the first time I've heard how hard it is to get metallic effect paint fixed without respraying the whole thing.
Glad I'll never drive, honestly... Brian