Bentley, Brabham, Aston-Martin, Jaguar, Lotus, etc. chose to race in the same dark green despite being very different manufacturers.
Matra, Ligier, and Bugatti raced in French blue.
Mercedes, Auto Union, and Audi went in silver.
Maserati, Ferrari, Alfa Romeo raced in red.
These teams often faced each other and did not share much love. Back then, sponsors weren’t really a thing for the cars, so they went with the national race color. The addition of stripes made it easier to identify particular teams.