purple region on 15 inch retina screen (mid 2014)

One day I noticed a purple region (few mm in size) on the retina display. I can only see it when the color of the images displayed are dark, for instance when displaying a black terminal window. Interestingly, if I move the mouse (which is black) over the region, the mouse image is displayed perfectly with no purple. Does that mean that this is software related ? Any ideas ?