There’s more to backlighting displays than just turning on a white LED

It's true that a mix of red, green and blue looks like white light, but it's not truly white light and I'd think there would be some cases where an item illuminated by rgb light would not look the same as it would under true white light, even though the rgb light itself is indistinguishable from the white - any comments?

Unless you are displaying photographs, the change in color balance with time is probably not an issue. This is especially true if you already accept the initial blue cast.

Measuring the output of an RGB light source in a display application is pretty trivial. Companies such as Avago make specialized color sensors designed to do exactly that. You still need to place them properly (easy on a display) and calibrate the system, but once done, it is easy to keep the color balance extremely accurate. I expect if you are designing cell phones, PDAs, industrial terminals, and the like, then you are likely very interested in white LED drivers. While these may represent absolutely massive quantities for the IC vendors, it likely represents a small amount of design engineers. However, many products do incorporate displays, they are increasingly becoming color, and they are likely LED backlight based....so maybe more engineers are interested. High powered LEDS for lighting also seems to be a growing field.