very good question. honestly, i don't know. but as with time, i think they improve the lifespan of all 3 oleds color. Maybe at first 15,000 hrs, then 30,000 hrs, and possibly eventually 60,000 hours and beyond...
i guess that's the reason why lg add a 4th color oled, white subpixel oled to improve the longevity of other 3 primary colors. white color is a mixture of red, green, and blue. by adding white oled subpixel, they can decrease the intensity of red, green, and blue diodes which improve lifespan.