Newer posts show what was learned on the 356 Registry site; that is me contributing there also.
I believe that the 6220 & 6420 are the same color, and were used for the Police vehicles.
The 6421 I came across in some information from the Reutter body book for the 911. I was able to search for the VIN and found it mentioned by someone. The car had belonged to a friend many years ago, and was scrapped long ago. It may be possible to chase that down a bit further. Perhaps I will get the Kardex to see if it lists a color in any way. My factory contact had no information on it.