Update to this thread....I finally got my spare set of wheels matched to the OEM Washi Grey centre caps that I already had.
Wheel Works in Crawley used a local paint specialist who came up with a standard Honda colour YR534M - Desert Silver. It is a lot lighter than the Pewter or Quantum greys and has a bit of a bronze tint.
Next conundrum is black or chrome wheel nuts...
Pictures taken under fluorescent light, so a little yellow.