Information provided by Brigadier General Charles McGee
The group transitioned to P-51 aircraft in July 1944. Indications are that some but not all of the P-47s had the tails painted red by the time they were replaced by the P-51s. I believe the group inherited both its P-47s and the first set of its P-51s from another fighter escort group in the Fifteenth Air Force.
Since the other fighter escort group already had another color for its tails, repainting the tails of the aircraft was necessary, since each fighter group had its own distinctive color or color pattern for its aircraft.
Those other fighter groups were all serving the Fifteenth Air Force before the 332nd Fighter Group began to escort Fifteenth Air Force bombers in June 1944.
A 15th Air Force message from Gen. Twinings office provided the identification policy for the assigned Fighter Groups P-47 aircraft as follows:
The 332nd Fighter Group did not paint the tails of their aircraft red until after they began to escort bombers for the Fifteenth Air Force. The first such escort missions began in early June 1944, and the group was flying P-47 aircraft then.
The P-38 squadrons were not to paint their twin tails. Only a few of the 332nd P-47s were painted before the switch over to the P-51 aircraft.
They arrived with red tail painted by the assigned Service Group. Perhaps there may be some history records that verify this information. I have heard other stories such as a pilot wanted more than the rudder in red and told his crew chief to paint the whole tail. The information is that this was not a task authorized for squadron level maintenance. The trim tab colors of the 332nd Group were done at squadron level for identification of the original three and later four assigned squadrons.