B5 blue was originally Blue Fire Metallic on the Plymouth brand and Bright Blue Metallic in the Dodge line in 69 and 70 and that's pretty close I think. I'm pretty sure B3 would have been Petty Blue (or in my case Basin Street Blue) but I could be wrong.
Here are the blue paint codes and names from 1970:
Code / Plymouth Name / Dodge Name
EB3 / Ice Blue Metallic / Light Blue Metallic
EB5 / Blue Fire Metallic / Bright Blue Metallic
EB7 / Jamaica Blue Metallic / Medium Blue Metallic
999 / Richard Petty Blue and any other special order paint
According to MyMopar.com, there was also a build sheet / fender tag option code for Petty Blue:
C37D (1970 only) Richard Petty Blue (Special Order Paint)