Replace the LCD if its bothering you, this is a manufacturing problem. But a replacement LCD may have the same problem. The graying issue is a backlight anomaly pertaining to the lamination of the LCD panel.
They're both just symptoms of usage and age. My 2011 has a few bright spot spots on it, and the backlights isn't exactly as perfect as it used to be. But for a 6-year-old laptop that's been dragged everywhere, it's not too bad!