Originally Posted by Pinguino
I noticed the greenish band of sky, here presented for your viewing pleasure. It is most noticeable just to the right of the model ship's headsails. Also, just left of the photo center, the color transition just above the lowermost distant cloud is a very light gray, with a very slight green bias.
This is not merely a matter of the camera and software. I see the color in real life, which is why I bothered to take this photo.
Most folks might not notice the green (or cyan, depending on circumstances), as it is very bright and nearly gray. My point is that the transition from orange to blue goes via yellow and green, rather than via purple. Might be different under different atmospheric conditions.
This is refraction caused by the water droplets in the air. Starting from the darkest top it is violet, then cyan, green, yellow, orange, and red. I would think that any gray you see are saltiating particles, for example how the clouds have a gray color sometimes, and this is most likely because you are viewing the atmosphere at some specific angle where this shows up. It is all the typical and invariable spectrum (the natural one not the paint one), which is what the human eye sees (dogs/birds etc see different colors), due to rods and cones if not colorblind, and are of specific radiation wavelengths 400-700 nanometers.