I wonder if there ever was a specific color of paint that each of the machine tool builders used. I know South Bend would paint a new lathe (or other machine tool of their manufacture) any color the customer wanted, at some extra cost. I tend to think that machine tool builders may well have started out with some basic color typical of that point in time- such as black, then later on going to a light gray or dark green. Machine tool builders, while conservative in their approach to design and much else relative to the machine tools they produced, were probably not immune to changing paint colors as times and tastes changed. The first generations of machine tools in the USA were often finished in black and had pin-striping and sometimes had scenes from nature painted on flat areas (such as on the side frames of planers). As things progressed, the pin striping and scenes gave way to a plain one-color paint job, often black. In an era when lighting in any kind of building was minimal at best, and what light there was, was often obscured by a forest of belts, the move to lighter colors for machine tools probably happened out of practicality. This may have been in the 'teens or 'twenties when more thought was given to improving productivity by improving working conditions. We take good lighting for granted, but "back in the day", an overhead drive shop was a forest of belts, and lighting was often bare incandescent bulbs with reflectors hung on cords at or near the machine tools. Windows were often plentiful to try to use natural light, as were skylights or "sawtooth" roof designs with glazing, but in nothing flat, grunge from the shop covered the glazing and cut down on the natural light. Somewhere in the 'teens or 'twenties, the realization that lighter colors on machine tools might improve working conditions took hold. Then, another school of thought as too bright a color on machine tools being a bad thing came along and the rich, dark green colors became common.
I've seen (and used) machine tools from the 1930's that left the factory with "buff tan" paint, as well as dark green paint, along with the "battleship" or "machinery" gray.
My own take on old machine tools is that they are meant to be used and produce work, not kept as museum pieces. I clean up my old machine tools, make the necessary repairs or adjustments, and put them to work. I got a 1943 LeBlond 13" Roundhead Regal lathe from an estate liquidation. The lathe was painted in an off-white enamel. In contacting LeBlond with the serial number, they told me the lathe's first owner had been a manufacturer of filters, local to where I live. That firm had spent WWII making filters and equipment for the production of penicillin and other pharmaceuticals. Whether the lathe was ordered with the off-white paint job, or whether the previous owner (dead about 12 years at the time I got the lathe) had scraped it down, prepped it and repainted it is something I never found reason to research. Once I put the lathe to work in my shop, hot chips and sulphur/lard based cutting oil have not improved the paint job any.
My old Cincinnati-Bickford "Camelback" drill is from sometime during WWI as it has dual metric/English depth graduations and was shipped with a 220 volt single phase motor drive. As near as I could determine, it was painted some kind of dull gray, much of which had been lost to wear. I scaled off the loose paint, washed the drill with degreaser, and hit it with some green paint as I always like the looks of green machine tools. I think the color may have been "Oliver Green". Like the LeBlond lathe, the old C-B drill sees use, and when I land a piece of structural steel on its table to drill holes, hot chips spiral off and more of that same cutting oil gets slung around, aside from the "total loss" oiling of the various bearings.
In use, my oily hands, often dirty from machining thru mill scale on hot rolled steel, weldments, castings and similar, leave dirty smudges all over some of my machine tools. I am old school in that I stand up to use my machine tools, even on long cuts. Years ago, if a person got the bright idea of sitting to run a machine tool during long cuts, the foremen would be on him in nothing flat, hollering murder. I might find a place to rest my left hand while my right is held ready to disengage power feeds or similar. The result is in the course of many jobs, my machine tools wind up loaded with chips, oily, and dirty with grungy hand prints. I was taught to never have a rag or similar anywhere near a running machine tools, so if I do wipe my hands and wipe the machine tool clean, it is between cuts with the machine tool stopped. More often than not, it is when the job is done with. About all I do when I am done working is clear the chips away, wipe the machine tools down, pay close attention to wiping the bearing surfaces (dovetails, bedways, milling machine table) and put some oil on the machine surfaces. If any of my machine tools ever did have a good paint job, it is long gone by virtue of use.
Another thing to consider is the fact that most old machine tools were repainted a time or two or three along the way. Some shop foreman or owner may have decided the shop needed to be "brightened up" and had the maintenance guys paint the machine tools in the color of the day. This could have been anything from a real good paint job to a "smear job" done with a wide brush and a bucket of enamel and a rag to wipe paint from where it should not have gone- after a fashion. Or, as was often the case, the machine tools were sold due to shop liquidation or retooling, and the machine tools wound up in the hands of a dealer. The dealers were notorious for "prettying up" used machine tools so they would look like they were rebuilt. Worn bedways and tables were cleaned up with emery cloth and then given a fast "flake scraping" or "frosting" to appear as if a proper rescraping had been done. The machine tools were washed with gasoline (back in the day), and any unpainted or finished surfaces were polished with wire wheels and steel wool. The cast parts such as beds, headstocks, aprons, tailstocks, etc were given a quick round of auto body filler to even out deep chips or missing original paint. This was sanded and then a coat of gloss enamel was usually brushed on. The color enamel used was a matter of what the used machinery dealer thought would sell, or what he thought the machine tool would "look good in". Typical colors were gloss light gray, buff tan, dark green, and now and then a medium blue. This was back in the "pre-Krylon" era, and the used machinery pirates had a crew of "mechanics" who did everything from moving the machine tools in and out of their stores or warehouses to the "prettying up". Those guys were good with a paintbrush and could lay on a nice coat of enamel that was free from runs and slopping onto machine surfaces. If any of those dealers ever gave a thought to "original factory color" it was likely a rare occurance, if at all.
My "two cents"- get the C-J lathe set up, levelled, make all necessary repairs and adjustments and get to using it. No one is likely to have a color chart or paint sample of the C-J "factory" color for the lathe, and the color of the lathe could have been anything at all even when it left the factory as a new machine tool. Pick a color you like and paint the lathe if you care to. However, if you use an engine lathe as it was meant to be used, taking hogging cuts on heavier work and using cutting oils, your new paint job will quickly be "broken in". The first heavy and hot chips to land on the painted surfaces will take the "new" out of your paint job quickly enough.
kidding 
