RPGMemes

Responding to your edit:

You've got it the wrong way around. What you see at sunset, the reds and yellows, that's the sunlight being filtered because those wavelengths make it through stronger. Your argument would hold there, if we do not count seeing filtered light as "seeing" the filtering material. (Although even that I'd question - if you hold a colored piece of glass against a light source so it's entirely backlit, would you say you're not seeing it?)

But the blue sky is not that. It is the air molecules being illuminated by light coming from somewhere else, and bouncing that light back into your eyes, with a bias towards blue wavelengths. If that does not count as "seeing" air, then you also can't actually "see" fog, it's the same mechanism.