If you get up way before sunrise and look to the East during nautical twilight you'll see that there is sometimes a band of the sky that is greenish. However, this occurs at a time when there is so little light that while your eyes cones can see the faint greenish band directly in the sky, there is not enough light reflecting off the terrain for your cones to respond and you only see in black and white with your night vision rods. Also, the light reflecting off the terrain is not just from the greenish band, but also the brighter orange band on the horizon, so the net color is closer to gray than green. So while the green in the sky is realistic, the terrain at that point should not be greenish; it should be in gray scale. It's kind of picky, however, to expect a game to model this aspect of human vision.
