If a simple power cut would work, there are remote power socket solutions:

https://www.netio-products.com...

Or DMX power sockets (DMX Dimmer with switch option)
https://www.thomannmusic.com/s...

If this is about the black level, which is not 'real black' if doing a full black on stage output, you'd try some display and output settings.
There could be several reasons for missing a 'pure black'. Hardware limits of the display/projector, color/brightness/contrast settings of the display, color/brightness/contrast settings of the output device, color/brightness/contrast settings of the distributing devices inbetween.

Regarding the output device, sometimes the 'black' a computer sends to the output, isn't really a pure black.
Posible reasons and solutions for it.

1. 

HDMI RGB level (full / limited)
This is a setting which has to be the exact same for the whole chain of devices.
It comes with different names like 'Video levels', 'HDMI Black level', etc . Some TV Screens only support limited RGB, some have an option to change it. Computer monitors always support full range.
MacOS doesn't provide a setting for this, as far as I know.

2.
Monitor color profile/calibration General informations (there might be better sources for it).
Windows monitor profile
Monitor color profile macOS

Default (some of multiple broadcast) profiles for TV Screens are Rec. 709 (Full HD), Rec. 2020 (HDR), P3 (UHD). High end computer monitors might provide higher level profiles, like sRGB or Adobe RGB.
Some Displays/projectors offer to select these color profiles. The profile settings should usualy be kept the same through the whole chain of devices. You might try different ICC settings to find the best fitting. Beware, that the colors might shift as well.

3.
manual calibration
there are several options to calibrate the color outputs manualy. from simple OS internal options, to hardware assisted ones.
Look for monitor calibration.

you could try with an Arduino board+IR and OSC

https://forum.arduino.cc/t/osc-triggering-ir-solved/597901 It is only an idea. I cannot make it by myself, it means I cannot help you to make one. But perhaps someone in the forum do.

Best regards, 

Jean-François

How about triggering a full screen black on the top layer in the meantime?

 @mrtsound Yes definitely try this before any of my suggestions. I didn't mention this because I assumed you would have already tried this.

How about triggering a full screen black on the top layer in the meantime?

stage-blackout.iua3

Does anyone know how to trigger a display into and out of sleep mode?

1.  Look at the manual for the display and see if it supports a way to do it.
2. Also look in the manual to see if the display can be setup to turn on when it receives power, as then you could figure out a way to turn the power to it off and on (though first you should contact the manufacturer to make sure this won't damage the display).
3. If all else fails, hook up an arduino with a servo so you can program cues that allow you to use the servo to press the power/sleep/wake up button for the display when needed.

Best wishes,

Woland