You cant see in it because there's no light ? Maybe some crude analogy to the first cameras dark chambers ? French wikipedia says it entered our language during WWII to describe enemy military strategies we had to analyze by interacting with them rather than reverse engineer from specs. Black is the color of the night and mystery, white of the sun and openness. I find it insane this is misinterpreted as good/bad, with the mystery color being bad.

We're fighting hard in my company against the same people as usual now brigadding to stop saying black/whitelist, because it does nothing to help black people in America (we're in Asia), who suffer from problems which go well beyond even white people: they entered a cycle of self defeatism where every problem has an external source and therefore solution, to the point of complete apathy.

So when a chinese says "this system is a blackbox" I will not, me a European, tell him to say something else because americans cant fix their shit and now need to pretend me and that chinese guys are part of their problem. It's THEIR problem, they fix it, and for real.