Can you paint Dow THERMAX WHITE FINISH INSULATION?
Thermax is rated for fire exposure and those particular boards are intended for interior finished space, so yes, you can paint the boards instead of covering them in drywall. However, I'm not sure the result will be very aesthetically pleasing or durable if this is going to be a finished residential space, which, based on your previous question, I'm guessing it is. But it should work.