The pyro 3,4,6,12 models were all painted by what looks like the same fella. Decals, similar paint work, coloring, etc. Probably the first wave, probably SUPER early 1976. We know the Blue 1 and Red Y were made in December of '75. I have a copy of the document that shows the time lines, and who worked on the armature/wiring/construction/paint, etc - it's AWESOME to see - and they worked on them up until December 24th, shipping to Elstree on the 26th.
I reckon that when they came back from the holiday break, they made those pyros, during that time when they took their time with the deco, and the "blue" call outs on the labels makes me think they hadn't realized that they would have needed to change to red markings, which again says that it was early enough that nothing had really been filmed against the blue screen just yet.