I think that I have looked into this once before and it seems that there are no proper codes for every manufacturer's alloy wheel colours. Worse than that, if you get your wheels refinished, its very much up in the air as to which "silver" they get done in "blueish" "greenish" "yellowish" - it seems they are all the same - the only proviso was "just get two done at a time and put them on the same side - no one will ever know the difference" - that didn't sound too good. Now that about 60>75% of cars get alloys factory fitted why can't they sort out the exact colour, then there is the metallic fleck partical size!