I notice that no matter how much you try to get your gamma to your liking, there will be that one mission that you find just does not agree with your settings. It's either the ambient world light is far off from what you are accustomed or the author's idea of lighting is just very different to yours.
Instead of enforcing standards or arguing with authors, how about putting more power into the players hands by letting them set an offset per mission? I was going to say you could set the absolute values but an offset from your main settings may be nicer?
P.S: Would be nice if the GUI sliders snapped so I did not end up with 1.11123234.
P.S.S: How about all graphical settings customised? Now users with lower-spec hardware would not have to remember to set their LOD settings back up after an intensive mission.