Now when I saw this with my 1520, i too felt that there is an issue at the center of the sensor.. but when I looked more carefully, my eyes too perceive the walls to have a green tint.. as a matter of fact the center of the image has the actual color while the rest of the image does not! Double check the room again, when the daylight bulbs are turned on the walls do look a bit greenish...
And as I told earlier, the center appears to be tuned to be work better with light and hence the color difference, its by design. I observe it in my Lumia 928 as well...
Now back to the purple hue, it will be a white balance issue only since I cannot produce it on all surfaces.. It ain't a hardware problem...