This may or may not be an error, but his beret is brown at the start of the film and becomes green before he loses it. But maybe he had two. It also is worn in a style that is most definitely not U.S. military. But maybe that's intentional. Paratroopers in the service (he's supposed to be former 101st Airborne) wore maroon berets, not brown or green. Special Forces wore green ones. But again, maybe that's all intentional.