My 1950s vintage house has the armored flexible conduit. Most of the
circuits have the standard black/hot white/neutral color scheme. For
some reason, the 20A circuit I want to modify uses a GREEN 12-gauge
wire all the way from the breaker to the hot outlet terminal in my
garage wall. I plan on changing that outlet to a double outlet to
eliminate the need for extention cords and/or adapters, and also add
another single outlet 10 feet away. That same circuit feeds some
outlets in my living room, I assume via a junction box somewhere in
the attic. Thankfully, they did use white for the neutral! Here's
what I'm wondering:

Should I continue with the green/hot color scheme for that circuit by
putting a wire nut and green pigtails on the green wire inside the new
double outlet box, and run a longer green wire from the wire nut to
the new single outlet, or simply change to the standard black/hot
wiring exiting the wire nut? The latter option would have the green/
hot wire coming into the wire nut in the new double outlet box, two
black pigtails feeding the hot sides of the two new outlets, and a
longer black wire coming out of the wire nut to feed the new single
outlet further along the wall. The neutral, in either case, would be
the standard white.

I can see the advantage of having the entire circuit the same color
(green), but it looks a little odd to have a green wire feeding the
hot side of the outlet(s) AND another short green wire grounding the
outlet to the sheet metal screw in the back of the outlet box.

No one except ME will probably ever see inside the outlet box, but
since it's semi-permanent I'd like to do it right.