I would agree with wt1 that this is a Scott #51, and we're looking at some major colour distortion. Notice how the white of the paper is decidedly pinkish in tone.
Just for fun (??) I adjusted the colour balance in Photoshop to remove the pink from the white of the stamp. And behold, a much greener image. Of course I don't know what the original green looks like (this is still very bluish), and we take into consideration the vagaries of our scanners and monitors.
But here you have it.
