I would need to order the production record from MMC to confirm, but I think that my '67 +4 is an example of "Smoke Grey (Light Blue) P339-0492." I've not seen another car with the same colour here in the U.S., but I have heard that the colour was more common for the European market.
It would be nice to know the CMYK or Pantone code for the colour, if anyone has it. Whatever it is, it is uncommon.