It's Japan. Those are Iwo based 51s from the 15th, 21st or 506th FGs that roamed all over Japan shooting things up when they weren't escorting B29s. The close ups are of a 21st FG P51D. Note it has rocket rails in some shots. The USAAF 51s used rockets against Japan but not in that set up against Germany.
For some reason it was much more common to use color gun camera film in the Pacific too.