“Rich black” in CMYK is one thing, but not what I was talking about. Am I misremembering that some really old inkjets used to be just “CMY” (or maybe a slightly different set of three pigments, but either way no K) where they had to mix all three to get an approximation of black, and do any like that still get made?
(It’s been long time since I’ve paid attention to any kind of printers other than lasers, LOL.)