> with a black neutral.
Interesting history of technical materials here.
Early US wiring was bare. To reduce death it was 100V. Soon delivered as +100V/0/-100V to give twice the power without twice the copper. The "0" was nominally tied to dirt.
Rubber insulation came a little later. (Metals and wires were more mature than rubber production.) The rubber was heavily cut with lampblack for toughness and economy. All Wires Were BLACK.
Interestingly as late as 1915 some argued that an UN-grounded system is safer. Easy to show in a lab. But in the wild there are no un-grounded systems. There is always some leakage, not enough to notice at the generator, but ample to kill a grounded person on the other leg. (Also longer lines with more lightning exposure fared very much better if frequently tied to dirt.)
That balderdash was cleared up. A groundED entrance conductor was first allowed and then required. And the inside wiring had to have that leg of the line "Identified". Since all rubber was black, the rubber was painted. Probably zinc-oxide, oil, and benzene to "bite" the rubber. Didn't cover or stick so well. Now we had the black "hot" wires and "Identified" (groundED) wires with bits of white/grey flaking off.
So:
Black = Hot
White(?) = groundED ("Neutral")
Sadly this crap paint continued long into the 1940s. Both my parents and I owned houses where the Identified wires were far from White and often pretty darn black. Sometimes we had to fall-back on the old plan: All Wires Are Black.
This is also sad because durable White Rubber was available in automobile tyre side-walls.
Like car rubber, electrical rubber breaks-down over the decades. My parents were lucky to sell-out before their rotting wired burned the place down.
PVC and similar plastics made the difference. Any color is pennies per mile cost, so all primary colors became available, and have usually proved durable inside conduit or cable.
FWIW, "Green" (groundING) conductors were rare here until the 1970s, though for a long time we pretended that metal armored flex was an OK Ground.
BTW: I have seen lots of gear where all the internal wiring was white. Utter madness to trace and debug.
