So I'm not the only one..
Thank you, ukael, for starting this thread. I bought this tablet mainly because I like to read in the bed and the no-lightbleed-possible OLED display was the single most important thing that made me go for it. So, yes, I was also a bit disappointed when I noticed that the text (white on black background) has kind of blue / red tint to it in one corner, and green-ish in the other.
I'm still wondering about whether I should get a replacement, but since I see that many others here report the same issue with their S 8.4, this is probably due to the limits of the manufacturing technology used and the new unit could possibly be even worse. And considering that the world is not overflowing with OLED display wielding devices yet, it is probably not an easy task to manufacture one without any flaw, so I can't really hold any grudge against Samsung -- it is still an amazing screen in many ways.
That said, it _is_ kind of annoying at times and I'm still thinking whether this could be corrected in software -- there are probably some differences between any two devices, but the main part of this problem is that the screen is too bright in the top-left corner and / or too dark in the bottom-right one* and each channel behaves differently (see attached pictures**). It could be possible to simply apply gradual gamma correction for each channel so that the dark areas get a "boost" and show up brighter as they should be.
There are already programs doing some color filtering magic, like CF.lumen, but I'm worried whether it would be possible to apply a correction in the form of a gradient -- uniform filtering of one color is one thing, but applying a gamma correction and deciding for each pixel what is the right value could be too GPU-intensive to make it a viable option. But I'm not an expert, so I keep wondering... Any ideas in this respect, anyone?
* My guess is that the display data connections are in the top-left corner (portrait mode) and the signal voltage simply drops too low before it reaches the bottom-right area. Since LEDs have a non-linear output dependence on the applied voltage, getting a precise light output level when it is nearly switched off is very difficult -- it reacts "wildly" to even slightest change in voltage, so it is not much of a surprise that the unevenness becomes worst at the lowest brightness setting / when using dark colors..
** First three photos are displaying R: 10, G: 0, B: 0 etc. at maximum brightness; the last one is G: 10, B: 20 or the other way around, I kind of forgot. All are using the same exposure 5 seconds and ISO 400. (The bright points are in fact white (menu buttons in ArtFlow used for testing), the green tint is likely just some weird effect of the lens in my camera.) The blue channel is obviously not affected nearly as much as the green and red channels and that's where all the color differences come from..