I don't think 'green' became a color reserved for the ground wire until sometime around 1955. Heck, 3-prong receptacles were more the exception than the rule, well into the 60's.
I've encountered several knob & tube installations where green was 'hot' and the neutral was black.
I've also seen buildings from the late 60's where the blue wires aged to appear more green than anything else.
It's also worth remembering that the practice of "always" including a green wire in our conduit is fairly recent. I don't think I came across that attitude until the 90's, and even then it seemed to be confined to California-trained guys. Even today, we can often use the conduit alone as the ground, at least according to the rule book.
