Is this a dead pixel or stuck pixel?
It could be dead pixels or it could be the driver 'chips' or a dead 'mux'. The hardware that control what pixels are turned on. Note the color, It looks to me like a group of pixels are 'turned on' when they shouldn't be. It is hard to tell just by looking at a picture. It could be anything in the graphics display hardware. Just let Apple replace it, no one troubleshoots to component level these days.