Really good effort as always. What do you mean by 'agreeing on the shade of Obsidian Black' with the body shop? Is this because the rest of the bodywork has faded a little?
So basically the car had a previous repair on the rear quarter which I noticed was slightly off in terms of colour compared to the other panels in very bright sunlight.
When I went to the body shop to get the bumpers and sills sprayed they took the code (197) and said that they have seen a few variations of it and had a paint 'book' where they had different shades painted on card which they compared to various panels to decide on exactly which mix to use.
As it happens one of the card matched the other body panels (the distinctive thing about this shade was there was a distinct blue fleck) and one of the other variations matched the rear quarter (which had a very slight red/brown tint to the base paint). So it seems there are a few variations in the paint - I'm not sure if it changed slightly during a particular year or what but obviously whenever/whoever repaired the rear quarter weren't quite as switched on about it.
As a result I unfortunately now plan on having both sides sprayed so I have perfect matching paint all over.