the 911 Turbo turns 50, fine, that's cool and etc... but, what I realized, is I haven't heard why Porsche 911s seem to have very good looking plaid upholstery. German car, Scottish cloth design - so that had me looking into that...

https://www.porsche.com/stories/innovation/porsche-911-turbo-50-years/

How the historic tartan pattern made its way into the latest Porsche anniversary collections? What does a fabric with deep Scottish roots have to do with Porsche?

Research reverals that the McLaughlin tartan was a design highlight of the 911 Turbo # 1, because  the chief designer at Porsche at the time, was going for a fashion look and wore a pair of tartan trousers to work...  Inspired by his bold style choice, the design team decided to explore how this classic pattern could add a unique flair to the interiors of their cars.

At the 1973 International Motor Show (IAA) in Frankfurt, Porsche unveiled the 911 RSR Turbo concept car, which featured an upholstery fabric inspired by the Black Watch tartan in a blue, green and black pattern. 

Two more patterns were soon added to the collection: the McLaughlin (also known as MacLachlan) tartan in a bold red and blue, and the Mackenzie tartan in shades of beige, red, blue, white and olive green. 

 The tartan interiors quickly became a distinctive feature of the Porsche high performance models

https://www.porsche.com/stories/culture/what-is-the-porsche-tartan-collection/