E6400 LED backlight screen problem

No, actually he is correct. These are not normal LCD backlight, they are extra strong so that if you have the sun behind (more or less) you, you can still see an image on the screen. If you a show gradient from white to gray, once you increase the brightness the gradient actually shift. The image itself doesn't move, but the screen is so bright that your eyes adjust itself in a way that you see less the complete gradient... which makes this "wash out feel" on normal images.
Beside at full brightness inside with standard room light environment makes it just impossible to continue to stair at the screen. 55-60% brightness is already very strong, if I move my eyes to look at the keyboard, let's say, I got my eyes adjusting.

 

I have the same panel on my T400, and its just a crappy quality TN screen. Nothing you can really do about it. Try adjusting color vibrance if that option is available with your GPU. As for brightness washing out colors, it is entirely not true. My desktop NEC made LCD screen is 450 nits and running it on max brightness or half brightness has absolutely no effect on colors or contrast. The LP141WP2 is rated at only 250 nits, but because of poor manufacturing or whatever it just looks like crap.