They do make a fibreglass body as well, but if you look at the pictures you'll see clear 'windows', and they do mention '2 mm lexan' if I remember correctly.
I presume the 'white' is the protective film most good body moulders cover bodies with - this is to avoid 'overspray' when the body's being painted.
It is generally only removed once the painting is completed - unless there's a particularly fancy body paint in progress - like I had done on my FG MT - the Ford phrasing was painted over the top ... I wasn't warned nor given the option.
Outlaw Graphics in UK wouldn't have painted it that way, but it's still holding up, amazingly!
Al.