Warshots are painted WHITE. There is a brown 2-inch band painted around the propellant section that indicates a live rocket motor. There is a 2-inch band painted around the warhead section. A blue band indicates the warhead is inert; a yellow band (sometimes with the explosive filler in black letters) indicates a LIVE warhead.
The Head Wookies’ Secret Service people should have known this and why the RN ship was “dressed” for a special occasion. This is not a state secret.
As an aside, during the mid-1980s, a USN missile cruiser and a Russian missile cruiser were in a friendly (neutral) port for a port call. The daily routine was to exercise the ship's combat systems for equipment checks. In this case, the Russian cruiser was aft of the American vessel.
One day, about half way through the port call, the Americans began their 0830 routine of running equipment checks. Someone in the missile house selected the wrong cells and loaded the launcher rails with two Warshots instead of the usual Pretty Birds. The on-deck safety observer immediately informed the missile house of the error and the Wardhots were quickly pulled back into the missile house, but not before there were a lot of binoculars staring at the loaded launcher from the Russian ship.
The American skipper called his Russian opposite number and offered an embarrassed apology that was accepted. Both skippers agreed to suspend weapons’ exercises for the rest of the port call.
I had a similar situation happen to me running DSOT on a DDG in port at San Diego. The safety observer didn't catch that live birds, rather than TSAMs, were under the launcher arms. As they were coming up, he SCREAMED to stop the loading. There we sat, with two live birds halfway in the magazine and halfway onto the launcher. The only way to cycle them back down was to bring them fully up on the rails. I think it may have taken an act of Congress (or perhaps divine intervention) to get the permission needed to do that. Definitely the most interesting DSOT I ever ran. (And yes, I did catch hell for letting it happen.)