What happened to Dell XPS 16 RGBLED screen (odd gradient discoloration)

I have a Dell XPS1640 with a RGBLED LCD.  Yesterday I took it with my to my car in which it was there for the whole day, when I got back home I noticed the laptop was very hot which I was a bit mad about as my settings are meant for it to go to sleep mode when it's closed.  It seems like it didn't do that as the battery was low and again it was hot when I took it out of the case.

Upon turning it on I noticed a weird wavy discoloration on the display, although it only shows up on black/dark images.  Up close it is basically individual pixels it seems that are showing, but from farther back it's this odd gradient wave.  Here is a photo of what it looks like:




Any idea what the cause of this was?  I am assuming from heat?  I am more interested in exactly what could have happened (I assume it is in regards to the RGB LED type of the display) and how is it possible for this to only become visible in black images?