I used to work for an MCC manufacturer and every now and again, we would get a Consulting Engineer on a project who INSISTED on an MCC being a specific color. They seemed to think it was OK to just paint them after the fact. It wasn't. As I recall (it's been over 25 years now), there was something in NEMA ICS or UL845 about not re-painting an MCC with any conductive material inside, so if you wanted a different color it had to be done pre-assembly.
One project shipped out and although we had taken exception to the color change, the contractor hadn't noted it in the bid and nobody caught it until it showed up on site, where the CE rejected it for being the wrong color (he wanted baby blue, it was hideous). So we had to strip out ALL of the units, panelboards, main and vertical bus bar etc.. We had it electrosatically painted in the field, which significantly cuts down the mess, but even using that process I witnessed exactly what weressl mentioned, the paint spray got EVERYWHERE inside that MCC and had there been any bus bars or units installed, it would have been all over everything.
I also had several end users paint MCCs after the fact, then complained about component failure afterward. The only one I have seen that didn't was painted with a roller and brushes, but that was just plain horrible looking. Even then I don't think ANY of them were foolish enough to have done it live.
Doing it live is a suicide wish. VOC based paint is a fire waiting to happen, water based paint is a flashover waiting to happen. Either way, I would not want anyone I know or like holding that spray gun!