BTW, the "black" on a CRT is almost a true black. The electron beam is off when the signal voltage is less/equal to the black level, there's no "black light" if the black level is perfectly calibrated. Displaying a black image fullscreen is indistinguishable from an endless vertical/horizontal blanking interval from a practical standpoint. There's a measurable decrease in power consumption, although it's not much (it can be great enough on a large TV, though).

On the other hand, VESA blanking mode turns off additional circuitry, and it can save a lot of power while still keeping the CRT heater on, suspending the screen without the disadvantages of a long wakeup time or stressing the tube.