Have you ever seen inside an OLED?
Yesterday, Mike was looking at some PCBs under the microscope, and happened to scan over the OLED while it was displaying a white image. He snapped a cool microscope video which I thought was interesting,
When the microscope zooms in, notice the LED matrix of individual red, green, blue LEDs. I guess it's confirmed then: Red, Green and Blue, at full intensity, actually does make the color white!