I dissagree with the black first. This is the tear down of my T/A. You can see in this photo the yellow was first then the black. Download the pic and enlarge it.
As with "mass production" of anything, cars, trucks, kids toys, etc,....there may be factory prints, procedures, etc, they all change as production gets underway, some are due to mistakes, some are due to "experimentation", or penny pinching as production is underway,...in the case of different blacks, for black outs,....might have run out of "that" paint that day, and substituted something else, or a certain procedure was done at another work station on the line and Gomer used the "wrong" paint, or what was substitued on purpose or accident 
,....back in the day it was Human intervention/mistakes on the line, not robots programed with a set of perimeters 
