Yes for OLED. Sometimes for LCD.
From what I understand, LCDs can have a resting state that will either stop light, or a resting state that will let light through. The backlight remains on, but a panel that natively blocks the light will require less power when showing black.
I could tell them that, and they would be rightfully pissed off. In most cases, though, a disabled person can figure out this puzzle, go on with their day, and not have to pay $1,500 for the inconvenience.