I originally purchased the high end 15" Haswell, that was a December build, week R. It was perfect, and a Samsung panel. But, it turned out to have a defective USB port.
I decided to downgrade to the base model, because Apple price matched a Micro Center ad (still running) with a $200.00 discount. The first replacement was a November build, week M, that had heavy yellow spots on the lower left and right sides. I returned it and received another, that was week N. It too suffered the same, except not as bad.
I called Apple support, and they wanted me to take it in to have a capture done. I wasn't excited to deal with the genius, but both he and the store manager saw the yellowing that I showed them (whew!). I asked the manager if he would pull another unit and explained the serial number week build coding. He came back with the newest build they had, a week V (50), December build (yippee!).
We opened it there, and I didn't see anything in store. When I returned home and put my clone on it, and checked it thoroughly, and the display is perfect. Bright, white, and no yellow tint, spots or banding. Panel is a Samsung A022. I can move on from this long thread, and enjoy my computer.
Best wishes to all those still suffering this issue!