Any wannabe telco guy can tell you that the green and red pair are called "tip" and "ring" respectively, most can tell you the historical reason why. That's not what I'm looking for.
As a baby boomer, I learned early that the yellow and black wires usually didn't do a thing. I know there are exceptions, for example lighted phones and party lines, but what names are used for these conductors?
There's no single right answer. I'm particularly looking for Bell System terminology, but I'm interested in any designation you can cite technical documentation for.
As in the 1970s, I want to yellow/black for power. Which polarity would you use?
Was AC ever applied to yellow/black, e.g. in the princess phones?
As much of the discussion on this question has focused on registered jacks, and misinformation on the web, I thought I'd dig up the legally binding definitions, in FCC Rule 69.500. That isn't easy reading, but really only RJ11 and RJ14 are relevant. I'll copy those diagrams and attach inline above. (to do)