If faces near the centre of your OLED TV have a green hue this is due to the red pixels there having darkened simply through use over time.
Don’t bother running the many colour changing patterns on YouTube to fix this. It won’t. Try to progress a warranty repair however if that fails or while it is progressing you can change 3 picture settings in under a minute to improve the picture appearance considerably.
Change colour temperature to cool, increase colour and reduce tint (the balance of green to red). I show this on my Panasonic TX-55EZ952B in this #short video.
If it works for you a comment, like or subscribe against the video helps share the info and support the channel.
GI Chow 
This solution doesn’t work on LG OLED. The burn is actually blue and shows mostly when something yellow is on TV, and it turns green as with a basketball court. When you increase tint the rest of the screen is now out of calibration. Setting warn to cool only enhanced the blue problem.
All OLED (apart from QD-OLED) panels are made by LG afaik and the video has over 600 likes so red pixel burn in looks like the most common scenario. If yellow looks green then that means there is insufficient red. If you look at each of the RGB pure colours full screen, is it blue rather than red which shows a dark (burnt in) patch for you?