Which takes more energy to produce, a white pixel or a black one?
My understanding is this: It depends on the device.
On a CRT display, a black “pixel” is one that is not energized by (any of) the electron gun(s). So in theory this takes slightly less energy.
In an LC display, the black pixel is one that is completely energized and blocks the back-light from shining through, and so in theory takes slightly more energy.
Printers use more ink the darker the color, and no ink for a white pixel, so black would use more energy, and more ink.
For some inkjet printers, there is one chamber for black ink on the cartridge, so whether it takes more to produce a black pixel depends on the model.
From a brief look at Wiki, it seems to be saying it even varies within the type of LCD screen you’re looking at, although not sure if all the LCD screens mentioned would be found on laptops or computer screens
As in some of them voltage needs to be applied to get to black, others white.
And then theres the kinds of screens you get on some of the new e-readers that dont need voltage to maintain their picture, so black and white are effectively the same.
Otara
Probably the biggest power consumer in an LCD is the backlight, so the actual savings of a black or white pixel might be negligible. Although, I could be entirely mistaken 
That’s correct. That’s also why the newfangled OLED displays are getting a lot of attention these days. Each pixel on an OLED display is a separate light source that can be independently turned on or off (or dimmed to an arbitrary level), so the black pixels don’t consume any power.
I thought this was always the case. Nevertheless, how could this possibly use less energy than a white pixel, which involves doing nothing?
You got me there.
Here’s a summary:
[ul]
[li]CRT: A CRT works by painting a grid of phosphors with an electron beam. A black pixel means no phosphors are being painted, so the electron beam can be very briefly turned off when it’s aimed at that pixel. So a black pixel saves energy on a CRT.[/li][li]LCD: An LCD works by selectively blocking a backlight. That means a black pixel is completely opaque to the backlight and while it is drawing power, it’s an absolutely tiny amount compared to what the backlight is drawing. A black pixel doesn’t have any effect on an LCD.[/li][li]LED/OLED: LEDs work by arranging tiny little light bulbs (light-emitting diodes) in an array. A black pixel means none of those diodes are lit. A black pixel saves energy on an LED/OLED.[/li][li]Plasma: Plasma displays work by exciting gas trapped in phosphor-lined cells. A black pixel means no gas is being excited. A black pixel saves energy in a plasma display.[/li][/ul]So it works in every display except the kind most people are using or switching to now. Since plasma displays are a dead issue, I hope OLEDs take off in a big way, but I’m not getting my hopes up.
Ben Franklin did not say, “Hunger is the best pixel.”