I worked on a school where they wanted all the EMT color-coded, five different colors. It was easiest to just have apprentices paint it all. Small rollers on long handles. Lay pipe over 2x4s. paint one side, let dry, paint other side. Not sure about the ground continuity after painting.
I would set up a stand with one by eights set 10 feet apart, with holes of various sizes drilled into the 1x8s, slide the ENT through so it is supported right at the ends, then take a paint gun and spray all of the conduit, rotate them all 180* degrees immediately and finish the spray. or you could build a stand that held the conduits about 3 feet off the ground, walk under spraying the bottoms first then come back and hit the tops. For the fittings, everything three quarter inch and above to be placed over a stick of EMT 1 trade size smaller then painted in the jig. Half inch fittings could be placed on a 3/8 inch wooden dowel or piece of all thread. 90s, sweeps, lbs, junction boxes, etcetera can all just be painted on the ground, let them dry, flip them over. You're looking at $10 worth of lumber if you set the 2 by 8 on the ground, maybe 25 if you build a framework put them at waist level. 70$ for a cheapy electric paint sprayer. $30 worth of alcohol, acetone, and rags to prep the outside of the EMT, and $50 for a gallon of good paint. I believe that two people could build a jig in an hour or less, and paint at least a thousand linear feet and Associated fittings per hour.
The ends of the EMT where the fittings go would not have paint on them as they would be inside the one by eight. Cut pieces, it would be a good idea to sand the paint off the ends to maintain good grounding continuity.
If you only have 200 feet of conduit through, better just go ahead and buy it pre painted. 20000 feet, you're going to save a ton of money painting it yourself. You also do not have to worry about it getting scratched up in transport.
I wonder though, with EMT that is exposed to sunlight, how much hotter would a matte black conduit be than a bare steel one? would one possibly have to derate for ambient temperature because of the increased temperatures?
