Update: I exchanged my phone
I exchanged by black Lumia 900 for a white Lumia 900. The new phone does not have the purple tint issue. It took some work to find a phone that doesn't have the issue. I had to go to three seperate at&t corporate stores over the course of three days.
The first thing I did at each location is walk in and set all the Lumia 900 display phones to LOW brightness. I then set my phone to LOW brightness. I then started a new text message on each phone and compared the keyboards. Most of the time the display phones will not have the purple issue or you may find 1 out of three with the issue.
Next tell the sales staff what the issue is with your phone. Every place I went into this week had no clue about the purple screen issue. Most people will be pretty accommodating and will easily do one swap out without any fuss. Unfortunately you may also encounter some people that will tell you that the purple keyboard in the text messaging screen is just a "feature." All you have to do is politely point out all their display models do not have this "feature."
Unfortunately in my neck of the woods there are a lot of Lumia 900s with the purple screen issue. So you may have to go through 3 phones at a location before you find one that functions as expected. Usually you will be told after two phones and certainly after three phone swaps they no longer have any in stock. I suspect in a lot of cases that is a lie but what are you going to do? Move on to the next location.
Try different colors. Be flexible. I went though something like 6 black phones before I tried a white one. The white one didn't have the issue. As the poll indicates there are problems across the product line. But it doesn't hurt to switch it up just for fun.
Interestingly the white phone I picked up this week did NOT have a green dot on the box. It had the latest firmware.
I don't know if that means anything.
The phone on the left is medium brightness. The phone on the right is low brightness. The color balance on my digital camera which I used to take these pictures was not calibrated perfectly for the lighting conditions. I can assure you though there is no obvious color cast on the screen at both settings. Problem solved.
One rather unfortunate thing happened during this saga. I went to the at&t corporate store located at 172 Deming St Manchester, CT. As usual when I walked into the store they had no clue about the purple screen issue. The salesman that helped me out did a full exchange BEFORE checking the screen. When he finally fired up the screen and checked it it was purple. I wandered off to give him a chance to rectify the problem. I believe he checked another phone and it had the same problem. The first issue is they should not do all the paperwork for the exchange before confirming everything works as expected. It's a waste of time.
After his first mistake the next thing the guy did was finally come back and feed me this BS story...
The white male sales clerk, who shall remain nameless, with a straight face told me he did some checking and that a message had gone out to managers that this is a known issue and that Nokia is working on a firmware fix that should be out in less than a month.
So this guy went from never hearing about the issue when I walked through the door to knowing exactly what the problem is and what the fix will be. Anyone else hearing this story or did I get filled full of bologna?
Anyway who knows what the issue really is. My philosophy is either return the phone and pick up a product from a different manufacturer or go out and aggressively try and find a working Lumia 900. I suspect once word gets back to corporate that people are coming in and trying out 3-4 different phones they are going to clamp down and start giving people BS about a "firmware update."