Precision M4600 LP156WF3 IPS display has colored spot
Hello. I bought a used Precision m4600 two months ago. It has LP156WF3 display, it's 10-pin IPS with LED backlight. After I started using it I noticed it had a green spot on it's display. The spot originates from the bottom left corner of the screen. Everything in that corner and around it is greenish. It's the most vivid and visible in the corner and along the bottom part of the left edge. It's like a drop of green paint spreading out on the surface. The green color spreads further into the screen area and fades away, gradiently. The spot is not pixelated at all, it's gradient and super-analog, it's not blinking or anything, it's always the same size. I can tell it's like 10% of the screen surface is affected by the greenishness.
So I decided to get another screen panel. I bought a new one from a local retailer, I believe it was unused, with the original minimal packaging and the screen film. And when I installed this new screen panel (by myself) it had the green spot too. The spot just was smaller and paler than the old one.
What is it? One or more LEDs light green instead of white and dispence the color around? So both my screen panels are somehow from the same flawed batch? LCD cable is worn out? Faulty graphic card? In country where I live the closest place the parts for old Dell models can be obtained is internet shops so my local services are willing to help me only after I buy those parts and they are delivered.