The picture below is from the delicious Mercedes-Benz Classic Collection 2004 catalogue.

Hmm. Some questions arise at this point. First of all, my friend is acquiring the fabric from M-B in Germany; they still make it available as upholstery fabric. He further informs me that it is available in four versions:
Blue Accent - Moss.
Red Accent - Fangio?
Green Accent - Kling?
Cream Accent - Herrman?
Before posting this thread I checked in the TNF archive to see if we had discussed the origins of M-B tartan and discovered that Eric McLoughlin asked the same question in early 2000, but had received no response.
So perhaps now, it might perhaps be worth trying again. What were the reasons for Mercedes-Benz adopting tartan for their racing cars? Are the accents described above correct? Which drivers were assigned which colour accents?
And when did it start? I have a copy of the 2 volume Lehbrink/Schlegelmilch book "Mercedes" (Könemann 1997) which shows a 1952 300SL (W194) with tartan upholstery. I also have Bill Boddy's book "The History of Motor Racing" which shows a W196R with upholstery that is distinctly not tartan. I cannot tell whether that picture is contemporary or not.
Presumably, Mercedes-Benz tartan finished with the withdrawal of the company from racing at the end of 1955.
So ... anybody?