I am happy about the lighting changes, I'd like there to be more contrast between settled and unsettled land - I should feel evil coming when I walk through unsettled lands. As a God fearing, freedom fry eating American, I'm in the #2 group, although it definitely has too strong of a yellow tint. I just played around with photoshop, and here are some more color options:

#4 - Using Autobalance Color Option

#5 - Making the Colors a bit richer (Sort of like #2, but less tinting)

#6 - Darker Shadows

#7 - Apparently Photoshop has a "Lord Xia" setting, strangely I didn't notice it before. Darkerer Shadows, with Red Tint for Maximum Evilness.
You have to be careful about making things too anything - too dark and its hard to read, too light and its hard on the eyes, too saturated and it looks too busy, too desaturated and it looks flat. Its also hard to exactly simulate the change - its easy to photoshop an image in ways that you can't actively render on screen. These are all full screen color adjustments, though, so I would believe that they could emulate them without too much hassle.
I would be afraid that with a post processing filter, as mentioned earlier in the thread, that it wouldn't blend with the ground when you can spin and what have. I know Tropico 3 has some awesome filters for screen shots and ambiance, but when you actually sit and play it feels like you are watching the game through a dirty window.