I think a big part of that is the conventional wisdom that a black interior should be an available option on any car. The fact that it was not an option seems counterintuitive, at least by today's standards. So when people see your interior, rather than being surprised it's black, they're surprised they haven't seen a black one before.
Totally agree. I mean two directly connected pieces of MN12 trivia that always surprised me is #1 black was not offered in 1989, and #2 that black was deleted after 1993 and green introduced in 1994. My desire for it to seem more extremely rare than it in reality is nonexistent, not just to trick casual observers but myself who knows better.
That's what truly great mods do. They blend in so naturally that you forget it was ever any different. My white cluster needles for example, I never think of those as a mod anymore.