In my experience, LCD screens do this with age, and it isnt generally noticed until another similar screen is sat next to it. They fade a little and get a slightly yellowish tinge, which ties in with you saying it looks 'warmer'
The later the model of screen, then the longer it takes for this to happen. The screen on my old Clamshell iBook looked terrible by the time I sold it at a couple of years or so old. My 12" powerbook is faring better, but still shows signs of this issue. But i just accept that this is what LCD's do with time. By comparison, my newer G5 iMac screen looks very bright with excellent very clean looking whites (Damn, I make it sound like some washing powder TV advert).