Another idea (which I've mentioned a couple of times elsewhere in this Forum). I credit this one to my father, who served on board an attack transport in the Pacific.
He - like everybody else who served in the U.S. Navy during WWII or since - recalled that the ship's personnel spent an enormous percentage of their time chipping paint and repainting. The first step in the process was to chip off the old, loose stuff. Then came a coat of primer, then the finish coat (grey, blue, or whatever).
The primer used by the U.S. Navy during the war was a sickly, slightly greenish, pale yellow - presumably a form of zinc chromate. (Dad recalled that one gang of enterprising sailors on board his ship tried to save some time by mixing primer with ocean grey, thereby producing a remarkably nauseous shade of green. The captain made them throw it overboard.)
This process went on constantly, virtually all over the ship - with the exception of the exterior of the hull, which normally was off-limits while the ship was under way. At any given moment, any warship that wasn't straight from a refitting yard would be adorned with lots of irregular splotches of that dull yellow primer, where the hands were in the process of repainting.
The trick in replicating this effect is to make it so subtle that it only shows up on close examination. I've done a couple of models this way, and they always bring smiles of recognition to Navy vets.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.