The nintendo games with so much colors aren't dark game worlds destroyed by warfare and stuff.. would make no sense in making Killzone 2 with Super Mario colors.. so it's all about the setting of that particular game

and the coming Street Fighter IV will be full of color, and Tekken 6 and Soul Calibur too, so it's all about the setting in which the game takes place, and some settings just can't use too much color..

did the op means FPS, because HD gaming is more than those types of games. From what i have seen the Unreal Engine uses the greyish color more than most . And as far i am concern, those games still look great.

 G-r-a-y is just as valid as g-r-e-y. At least in some dialects of english.

People who say it makes it look more realistic have to go outside and tell me if you don't see colors. Even in ruins such as games with gears of war there is still color. It's not purely grey like some hd games.

Yeah, I know, it have colors alright, but its blurry its so blurry that even the morning scene was like its raining even it wasnt raining.

http://www.gametrailers.com/player/15068.html

Ah, but ssj12, I think I disagree.

I believe Gears and Killzone both use a filter, just like MGS4 did, that make every pure color in the game have an overtone of the color of that filter. The problem isn't that the environs in real life lack color, they certainly don't, again I point to blood.

Another thing, these enviroments don't exist in real life. If Killzone or Gears had say, a giant flag blowing during a level, with bright red colors for blood, then that could change my opinion, but even look at the sky, it is greyish.

Bioshock and Halo, both of these games have excellent color schemes and don't resort to grey filters. I agree that the grey problem isn't major, except in Gears, Killzone, and maybe Resistance, but let me show you some screenshots:

Now look at Halo 3

And Mirror's Edge

And bioshock

Now I ask you. Why the grey? It certainly takes away from the impact of the graphics, imo.

Edit: Obviously that is a tech demo for KZ3, but the new screens are just as grey, so bear with me, the ss doesn't matter, but the point stands. Why do developers find it necessary to use grey filters to present realism? 

so we can say that the Fighter, Platformer, Adventure, RPG and some other genres actually consist mostly of colorfull games, only the Shooter genre has got some grey games, not all of them even, and Silent Hill is also dark and grey but you can understand why

Yeah, certainly. I'm also saying that the grey takes away from the otherwise excellent graphics in some titles. Grey or green filters work in some titles, like Silent Hill, MGS3 and 4, but in most others they just seem generic, drab, and boring.