I think you'll find that's the limitations of the printing process, combined with the lighting when the photos were taken. Take a closer look at the photo on the right of the page - although there's a slight green colour cast, if you look 'through' this, you'll see the grey and base metal tints. The colour cast could even be the effects of lighting in the room where viewed, reflecting off the inks on the page.
I've looked at many, many jet exhausts over the years (I know, it's sad!), including the J-79 on, for example, Phantoms, and I've never yet seen a green example, they've all been a metallic grey shade, with some exhibiting a slight pinkish brown 'haze' where oxidation has occurred if left out in the open at, for example, a museum.