Does anyone know what causes this uneven pink hue to occur in the LCD manufacturing process?
Yes. Uneven white balance is a result of alignment problems with the shutters, filters, polarizers, or backlight in the affected region. "White" on a transmissive TFT display is a result of all three subpixels being switched fully "on" and allowing the white backlighting to shine straight through. If the backlighting is not consistent to the same color temperature, you'll have uneven colors on the screen. With older CCFL backlights, this was easier to spot, because you had typically 1-3 lamps on the screen. LED backlights have many more elements, and can therefore be much more blotchy if there's pronounced unevenness in the backlight. Every individual backlight bulb, even of the exact same model, has a slightly different color temperature; you usually just can't perceive the variation.
But it's not always the backlight, either. When one or more of the filters or polarizers is out of whack, even a perfect white backlight could show as slightly off-color.
There are many ways this can come about, such as thermal or mechanical stress, very minor voltage variation causing the crystals not to "twist" or switch completely on, backlight leaks and bleeds, slight physical misalignment of the various layers of circuitry, pixel elements, polarizers inside the display.
Oftentimes displays even themselves out over time as various elements break in (just like you can sometimes fix stuck pixels by rapid cycling colors), and sometimes they don't. Considering that each pixel is built from close to 10 separate pieces, the display alone has 30 million parts. At least a few hundred of them are going to work slightly less than perfectly on every single display on the shelf. Some are more visible than others, and that's true even of units that fully pass QA.
