Just to confuse matters, here's Qo'noS in 2151:
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And here it is again in 2367:
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Pollution ? Different planet ? Visual effects mistake ? Taking all bets, I also offer video poker!![]()
I'd either chalk it up to the long-term effects of the Praxis explosion on Qo'noS's atmosphere, or to a simple change in atmospheric appearance on the basis of the relative position of the observer. They're both greenish; I wouldn't consider the differences sufficiently minor to care overly much. You might as well wonder why Earth looked different in Star Trek: The Motion Picture vs. Star Trek: First Contact.
Shots of the planet's surface show very different atmospheric conditions as well.
Well, it's unreasonable to expect the atmosphere to look the same from everywhere across centuries of time. Earth's sky will look very different depending on what the weather's like and what time of day you're looking at it, after all. Besides, the capital city in ENT was clearly different from the First City, so ENT probably presented a different location on the surface, too.