Warbird Information Exchange

As for "wolves in sheeps' clothing," I've heard of at least a couple of instances in which Japanese aircraft were painted in Allied markings. One was a paratroop operation early in the war, in which the transports (Japanese copies of the Lockheed C-60) were painted with American insignia to fool our forces into not shooting at them. Then at the close of the war, the submarine-based Aichia Seiran seaplanes intended to bomb the Pnanama Canal were supposedly painted in American markings. That operation was aborted when the war ended, and the planes scuttled before the subs returned to Japan.

On 26 June 1942, a Catalina flying boat of 11 Squadron RAAF was about to alight on Havannah Bay, New Hebrides (now Vanuatu), to refuel. The ‘Cat’ had called in there on its way to bomb Tulagi in the Solomon Islands, and was then on the return flight to Noumea having completed its mission. Despite its presence being expected, the American ground control at Havannah Bay had, as a precautionary measure, ordered a US Marine Wildcat fighter into the air to identify the incoming aircraft.
Geoff Pentland, in his book RAAF Camouflage & Markings 1939–45 – Vol. 1, takes up the story:
This the US pilot did, but though the shape of the Catalina was no doubt disturbingly familiar, the red in the upper wing roundels [national insignia] seemed to him so distinct—as he later said—that he mistook them for Japanese markings and immediately attacked. Bullets passed through the Catalina’s main crew compartment, fuel tanks, and ailerons, but fortunately no one was hurt and the aircraft was able to land safely.
Flying Officer Robert Seymour and his crew were undoubtedly shaken by this close call, but the incident had a more far-reaching consequence. It was decided that operational and second-line RAAF aircraft were henceforth to have the large red centres of their upper-wing roundels painted out in white. This was formalised in Aircraft General Instruction C11, Issue 4, dated 31 July 1942. Within a few months, the order was extended to all roundels on all RAAF aircraft.
Ironically, the Americans had already foreseen the problem. Firstly, prior to Pearl Harbor and again in 1943, the US national insignia was deleted from the upper right and lower left wing surfaces in a similar attempt to differentiate its aircraft from Japanese (the latter displaying the red Hinomaru disc on all four wing surfaces). It was believed that the position of a marking could be the first indicator of friend or foe.
However, in practice, colour appears to have been the more important signifier. From a distance, red can be seen more easily than other colours—often, in fact, before other details of a marking can be made out. Cases of mistaken identity led, in March 1942, to the red disc inside the US national star being deleted. On 27 March the operations diary for 13 Squadron RAAF reported:
Orders issued by the US Air Staff to the effect that the red circle in the American insignia on all United States aircraft was to be immediately painted white to avoid mistakes in recognition, particularly by ground troops.
Considering the above, one might ask why red was still in use on RAAF aircraft six months into the Pacific War.

As for Vietnam ...... no matter how damaged an a/c returned from a mission, he ordered it on ops next day...... so ground crew became inventive and started to paint the 'correct' tail-number on a different but serviceable aircraft overnight