Except tantalums!
I expect it was to mimic the outside foil mark on dog bone caps. Black mark goes to ground (usually).
I don't think I've ever owned a Japanese multimeter. I just have American and Chinese ones.
Life would be simpler if the early electrical guys had guessed the right sign convention for current. That and QWERTY are the only ones that come to mind right at the moment, at least in my lab.
Cheers
Phil Hobbs