Since the first USA machines built were in the WWII era, I always suspected the color was not so much a decision as a case of having bunches of OD paint available and nothing else. I know at my first job, all the REEDs were army green, and all the Stokes Plunger machines of early 1950s vintage were flat out battleship gray. Looking down the production line there was like looking across the motor pool at the local Army base. Toward the end of their run of prduction in the late 1970's Stokes made the big move to let customers pick their own colors, as long as the choice was Gray, Green, or hospital white. Seems like that big range of color schemes still holds the high ground even today, except for Beige/Tan on a couple brands.
Best I ever saw though, were some machines at a custom molding outfit that did lots of work for Audio/Stereo equipment customers a few years back, who had all their presses done in metalflake candy apple red and emerald green. Very high gloss, very impractical, but great fun compared to the dull flat enamel on every other machine around, even today.
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