Original '71 Duster Twister color options are ??

Pretty sure Twisters were available in any color in the Duster color chart. If you are doing a color change, I would not even worry about it being period correct, pick a color you like and go for it. For instance, since your car is a 71 and Joe mentioned Petty Blue, if you like it do it, even though Petty Blue AKA Basin Street Blue was a color introduced in 1972.