To be clear, I'm not an electrical engineer, nor do I claim complete knowledge of how displays work.
However, I have done research into displays (televisions, computer monitors, AMOLED phone screens) out of curiosity, and wonder why OLED technology and a white source aren't used in complement.
A quick (and over-simplified) rundown: LCD displays use a backlight (commonly LED these days) and Red/Green/Blue color sources to display color. However, this approach is inefficient at displaying dark or black colors because the backlight has to be bright enough for the brightest color, and then cover up the parts that are darker, which is why even a black screen seems to glow. OLEDs self-illuminate, so they don't need a backlight and are generally much more efficient (and more color-correct), and better at displaying black. However, OLEDs can use significantly more power than their LCD counterparts when it comes to light and/or white backgrounds.
Would it be possible to add a white source (like an LED) to OLEDs to essentially combine the energy efficiency of both types? If so, why is (as far as I can tell) it not being done?