A phenomenon that happens to all LEDs when they are over driven.
Heat and strong blue light bleaches the yellow phosphor that makes a white LED appear white. When the phosphor fails, the LEDs turn blue.
Here is an example on a 3 year old 4k LG television. This type of faliure can be prevented by turning down the backlight to a reasonable level, but unfortunately most people use them how they come out of the box, cranked to full, and this is the result.