I've just received my first replacement handset as the previous one was very grainy on low brightness and had a purple tint. This replacement handset is worse than the last, the backlight is brighter at the bottom of the screen and gets darker as you look towards the top, an issue my previous handset didn't have.
Anyway, I'm exchanging the phone for yet another one and hoping the display will be okay.. On this call however I mentioned this thread and have given the rep I was speaking to the URL which he will give to one of the managers at Phones 4u HQ and they will look/investigate the issue further. I don't know how much this helps but I'm hoping for something at least.
I will update once I receive my 2nd replacement in around 5-6 days.