You can't really compare the graphics fairly, because where both Playstation 3 and Xbox 360 both shine are their exclusives, which you can't compare side-by-side. I mean, Uncharted 2 and Killzone 2 right there are graphically amazing games.
Clearly, the colors on the Xbox 360 versions are much more grayed down and not as rich as Playstation 3. I don't see why people think this is so close, or even worse - saying Xbox is better...
Greelax's comments