TL;DR short answer
To protect PSU’s that failed catastrophically during Hipot tests in factory, I modified the HV supply probe to insert a string of 1/4W Resistors so if it failed the xx uA limit the capacitance would not dump amps into the device. You ought to consider doing the same at exit after parasitic capacitance, and use static dissipating material to safely discharge until to get experience.
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There is not enough detail known on the leakage resistance of the medium, effects of humidity and air contaminants that affect leakage resistance nor the volatility of an organic paint.
What is interesting is that Electrostatic Spray Deposition shares the same abbreviation as Electrostatic Discharge, namely ESD. Spraying nano particles of paint while the volatiles evaporate during air travel sounds like an opportunity for combustion if the current is too high. But like Hydrogen the explosive limits LEL (4% fact) and UEL (lower and upper) determine the probability of explosion. For concentrated organic paint, I would hope the concentration is above the UEL.
However you question is limited to the residual charge of the HV paint gun, and again this is unknown due to ambient conditions of humidity and dust that determine the decay time constant of some unknown purity of a dielectric insulated paint.
If in doubt use a sheet of CMOS carbon black foam or other static dissipative material and any charge will bleed slowly..
It is also interesting to note that powder coating version of ESD use a grounded nozzle to spray and a UHV charged conductive target that can easily be dissipated using ESD dissipative material or controlled humidity.
I recall not too long ago doing UHV 100 kV DC insulation tests on a 5MVa transformer to determine that the inception voltage for Partial Discharge or PDIV was around 18 kV which was below the HV primary side and resulted in H2 generation in the oil filled transformer. The fascinating part was as we were guarded by a Faraday wire cage that was grounded standing outside 3m from the massive transformer in the factory, the epoxy paint on the transformer tank and the Safety cage both got electrically charged like a nylon carpet and gave vigorous impulse shocks just rubbing or touching the paint everywhere on the surface for a couple minutes. It also made any dry hair and the backs of our neck “literally” stand up.
I don’t have any powder coating experience, but have never heard of any issues, but I’ve given you some variables to think about, like charging the target instead of the sprayer and grounding the nozzle for safe neutralizing and direction control. As well variables that cause charge decay ( air contaminants and humidity)
I think monitoring the HV current level and a AM radio to listen for paint PD discharges on a quiet AM band will give you the best feedback for charge control in your ESD paint research.
There are also thousands of articles on this subject to follow, more often focused on nano-deposition for semiconductors. So Socratic filtering of your re-searches is necessary.
Also read about ESD protection with 1Meg resistor to shoes, and static dissipating lab coats to see if this applies to ESD Painting.
REF
http://www.wermac.org/safety/safety_what_is_lel_and_uel.html
https://www.google.com/search?q=Electrospray+Deposition+paint+powder+coating&tbm=isch&ved=2ahUKEwjugM2yufHvAhUJYKwKHW5gD7sQ2-cCegQIABAA&oq=Electrospray+Deposition+paint+powder+coating&gs_lcp=CgNpbWcQA1DEpQVYtscFYLnIBWgAcAB4AIABpAGIAeYKkgEEMTQuMZgBAKABAaoBC2d3cy13aXotaW1nwAEB
