Battlefield 3's got some of the most realistic visuals on the planet, and a lot of that comes from the game's use of lighting. It washes out colour palettes like the desert sun at midday.
Some people like that, but others don't, which explains why there's now a little hack available that removes the game's colour grading. Your mileage will vary on how effective it is - I think it makes it look more like a video game - but then, I'm also a sucker for big blue skies.
There's a slight problem with using it, though: because it's technically a hack, if you try and use it in a proper, authenticated game, the system may well think you're doing something naughty and boot/ban you.
So if you're going to try it out, try it out in private with pals.