If you are a fan of the Always On Display feature and you own an OLED-powered smartphone, one of the rumored upcoming features to the brand new Android 9.0 Pie will definitely excite you.
Fellow colleagues over at XDA Developers found some interesting strings in the Android 9 source code hinting at enhanced Always On Display feature. According to the code, in one of the future Android Pie updates, you will be allowed to set a wallpaper to the Always On Display and it goes without saying, it will turn it into black and white to consume less power.
The code also reveals that the cross-fading animation is 400 milliseconds long and the wallpaper will disappear after one minute. But that's just the default setting, so customization will likely be possible.
Unfortunately, we don't know which update will bring the new functionality and whether the existing Pixel devices will get it soon. Our best guess is that the Pixel 3 and Pixel 3 XL will end up with the new feature first.
Symbian did that on 2011 / 2012 My N8 and after that my 808 had a feature that acted like that.
Samsung Galaxies already support images on AOD
You are partly correct... For LED, Black is no consumption and for White it's only for the pixels it will light up. Whereas LCD will be constantly consumes energy for whole display.