For B3 I believe you have the Plymouth color sheet there = "Basin Street Blue"; Dodge was "Blue Streak" (or "Super Blue" on Chrysler charts), but same color. Just like calling a FC7 Cuda "Plum Crazy" brings out the pitchforks from some folks.
I guess its actually TB3 (replacing the EB3 poly of earlier years), commonly known as "Petty Blue" or "Corporate Blue". I think it was only special order code 999 on the fender tag in earlier years, but later years I think it was part of the official palette like here in 1972. I'm not 100% positive on the history of this, but have seen earlier Chargers/Dusters this color.
It's definitely not B5, as that is metallic (poly). If its original paint, 45 years can play havoc with the tones.