I agree that recent FPS games have failed to impress, but the problem is less about a lack of colour and more a lack of imagination, particularly in the weapons and guns.
In just about every shooter I have played, no matter, how colourful the environment, you can guarentee you'll be using a pistol, machine gun and shotgun. There's a very good chance a rocket launcher and sniper rifle will show up, and perhaps a cool but useless gimmick weapon thrown in for good measure.
As for enemies, they'll almost certainly be human, or at least humanoid. They'll mostly use machine guns, but they might have some special units:
>A guy with an explosive attack.
>A heavily armored guy.
>A sniper (who telegraphs his location with a red laser beam)
>A guy with a jetpack. He spirals out of control and explodes when you kill him.
>A guy on a turret (which you will inevitably turn against his comrades)
>A lightly armored asassin guy, who uses melee attacks and moves like greased lightning.
>A crazy guy armed who charges at you and explodes.
>A swarm of weak guys, who will attempt to overwhelm you via weight of numbers.
And before I forget, your character is always either part of a military unit (maybe a SPACE military unit if you're lucky), or a lone dude who is either mute or overflowing with cheesy one-liners.