Are there not laws regarding the use of false markings on military aircraft in international or foreign airspace?
While it may be against international law to "operate" in false markings (and a definite Geneva violation if the intent is to subterfuge in times of conflict), I believe it is not unheard of to have aircraft at big shows painted to look like a future operator or a potential customer. Air chiefs and polititians love to see potential aircraft in "their" colors. Usually the plane is flown to the show (or shipped as air or sea cargo) in normal markings and they recieve a quick repaint or roundels once at the show. Or roundels are taped over. Many display aircraft are actually leased back from the military branch to the manufacturer and flown at the display by company pilots. I am sure lots of lawyers are involved, and I can not imagine the red tape if one on lease back got bent.