NPS bought the light green vehicles maybe in the early '80s. I think Fish & Wildlife did too so maybe all Interior Department did, as did Natl Forest Service (Ag Dept). As I recall our patrol vehicles by then were white with the green stripe. By '86 NPS had gone to the tan paint (almost beige) and then at some point a bean counter or angry politician decided that standard factory colors were good enough and we got whatever color was offered cheap - mostly gray, silver, or white.