Rich:
You left one out.
#212 is a Combine, not a coach.
The fourth of the first Silver & Gold Coaches and probably the first coach so painted in 1950 was #280, which is now in Boulder.
The first three coaches painted in the new scheme were #280, #306, and either #284 or #320. One of the last two was not repainted until at least 1952, and maybe 1953. The reason I am sure of this is the distinctive 3 sets of lamp vents on 280, which actually ran in the San Juan consist in the fall of 1950, and the flat home made vent covers on #306. #284 and #320 have identical vents.