Rufus,
Welcome to the Forum.
You are correct, all Triumph motors were painted black.
I do not have a "concours" TR6, but rather one that is modified and improved for safety and performance, therefore I chose to do the engine in red. If I was a purist, it definitely would have been black. But if you look at my website, you will see that I'm far from a purist.
And I just think that having it painted black is boring, but that is simply MY opinion and carries no weight except in my garage.
I think that some of the guys here refer to these as "Resto Mod" cars.