Just noticed your earlier reply.
You have reseated the video harness connections at the motherboard end, and on the back of the LCD panel itself with no joy. You have confirmed that the graphics is not at fault, as you are getting a normal image on the external display. Your inverter board and backlight are not at fault, as the laptop screen is white (not dim or faded) therefore these are working fine.
From what you have said, then I would say that, unfortunately, your laptop LCD panel seems to be at fault.
You could possibly try to pick up a cheap LCD panel on Ebay or somewhere on the internet. Sorry not so cheerful news for your laptop!