> Quote - Illustration on the left: Because we know that the sky adds an ambient blue color to everything, you can simply subtract the light blue sky color from the photo, like i have done in the lower left of your image and it reveals that the moon is, in fact, orange!

No you cannot simply subtract. First you have to take gamma correction into account. That photo is not recording linear values - they are sRGB values. This really matters here. You cannot directly perform addition or subtraction of sRGB values. You must use linear values.

Here is my screen shot from Poser Pro where the material room has automatic GC. You can see quite clearly that after removing the blue glow from the atmosphere, the moon appears yellow, just as I said. I also used an HSV node to amplify the color and make it more obvious.

Now it is not actually yellow - it is gray. It is the sun light that is yellow.

Also, before we do any more of this, everybody please pay attention to this simple fact:

The color of photos is arbitrary. There is an element to the internal processing called white balance and unless you undo that you cannot actually find the true colors.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)