DELL 2407WFP Color Gradiant Issue

My Dell 2407WFP came with my system which I purchased in Nov 2006.

Recently I see its having warmer colors on the left and cooler colors on the right. Meaning if I open a blank white window and drag it to left, it will apear slightly brownish and if I drag it to right, it will apear slightly blueish.

First I thought it was the video card, so I switched from a resonably new Geforce to a ATI. It still seems to exist, even after VGA to DVI connection changes.