Microwave communication dishes are painted routinely. Not metallic paint of course. To prove it to yourself do a before and after signal strength test. Find your weakest signal and compare it. As a telecommunication tech with 40 yrs in the field I would not hesitate to paint mine.
H/R Endeavor 2008
Ford F150 toad >Full Timers
Certified Senior Electronic Technician, Telecommunications Engineer, Telecommunications repair Service Center Owner, Original owner HR 2008