CRT - Black didn't light up the pixels (I don't remember the details as to how), so it did reduce power usage some.
LCD - Had a constant backlight (see sibling comment for details), so there was little to no difference between black and anything else.
OLED/AMOLED - Black LEDs are actually turned off, instead of displaying a dark color, so we're back to it saving power - more even than CRTs did.
Just a detail that isn't quite right in the article: black is actually the highest power state for LCDs. The backlight draws the same power all the time (for a given brightness setting) but the pixels draw more power when they are black.
CRT - Black didn't light up the pixels (I don't remember the details as to how), so it did reduce power usage some.
LCD - Had a constant backlight (see sibling comment for details), so there was little to no difference between black and anything else.
OLED/AMOLED - Black LEDs are actually turned off, instead of displaying a dark color, so we're back to it saving power - more even than CRTs did.