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A monochrome monitor displays only one foreground color and one background color. Usually the monitor was manufactured to produce only one color, which was cheaper (both CRT and electronics) than a color monitor.

Was there a monitor that accepted a monochrome signal, but then allowed a choice of foreground (or background) colors? For example, had an option to choose between green-on-black and amber-on-black?

Inverse/Reverse video is not the subject of this question.

This question is asking about such a capability in the monitor, not in the computer. Certainly, there were many computers that sent a color signal but had monochrome display modes with configurable colors, but that is not the question here. This is not about having several monochrome modes generated by the computer.

Related:

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    One important feature of mono displays was that they didn’t require a shadow mask (which ensures that only the phosphor of the appropriate colour is exposed to the electron beam from the corresponding gun) and so the images could be much sharper; cost wasn’t the only consideration. – Frog Mar 25 at 5:23
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    Some experimentation was done using white phosphor flashing at certain rates to generate the illusion of colour. This never caught on because it was much more effective at generating the illusion of nausea, and probably epilepsy too. – Frog Mar 25 at 5:25
  • @Frog Shadow masks would also warp when G-forces are applied which badly messes up the color. That's why avionics typically didn't use shadow-masked monitors. See my answer for more. – Alex Hajnal Mar 25 at 5:25
  • Not quite what you’re asking for, but at one point I had an EGA monitor that had a “monochrome” button on the back. As I recall, it would blend the color signals onto a green-only signal. I don’t know what the use case was for that. – Euro Micelli Mar 25 at 8:58
  • The Vectrex allowed users to change the color of the monochrome screen by placing overlays upon it. For games with a rather static screen layout, this made it possible to have different regions of the screen show up different colors. – supercat Mar 25 at 18:02
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A form of this was used extensively for avionics displays. Known as the penetron (stop giggling), the CRT used a single gun and dual phosphor coatings (red and green). Each frame was drawn in two passes. In the first, low intensity scan the inner phosphor layer would be stimulated (generating, say, red light); a second scan at high beam intensity would stimulate the outer layer (e.g. green). Stimulating a point on both passes would generate a blend of the two (e.g. yellow). Note that each pass is a fixed intensity (not greyscale) which results in three possible full-intensity colors on the display (plus black).

penetron tube
Source: Lamps & Tubes

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    Hope you don't mind that I added a picture. It was hard to find, as most pictures of "penetron" are for a brand of cement. :^( – DrSheldon Mar 25 at 6:00
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    I normally knew them as Beam Penetration CRTs. We used them on flight simulators in the 70's and 80's. Mainly night visual simulators where daytime scenes didn't have to be created. They worked well for that. – Kevin White Mar 25 at 17:12
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    This sounds like the what the x-wing targeting computers in the original star wars were based on. Yellow grid with red targeting information on a black background. eg. google.com/search?q=x+wing+targeting+computer&tbm=isch – Luke Mar 25 at 20:18
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    @Luke The ones shown in the original movies were undoubtedly hand-drawn but yea, that probably was the inspiration. – Alex Hajnal Mar 25 at 21:06
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    @Luke Username checks out. :) – void_ptr Mar 26 at 21:39
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Yes, back in the day my family had an IDEK brand color CRT that supported setting the color of monochrome signal. It was not a standard PC monitor for VGA only, as it supported both analog and digital inputs, and went down to 15 kHz as it was used with an Amiga as well.

In the front panel there were three buttons for disabling each component of RGB individually. When the monitor was configured to accept MDA/Hercules signal which is digital monochrome signal, the color is white and you can then select which RGB guns to disable to get e.g. green only picture.

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  • I had an Ancona 80 14" CRT monitor (originally bought with a MSX-1) later also used with a Amiga 500. This was color (composite video and CVBS input) but could also be set to Amber and Green. Same monitor (rebranded) was sold by various other companies (Philips, Commodore itself and Atari). Was actually made by Philips. All variants used the same basic design, with different input connectors and casings. Philips even had a 14" TV based on the same thing. You could buy the TV tuner module as a spare part and plug it in an internal connector on the PCB monitor to upgrade it. – Tonny Mar 26 at 13:00
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I have a Eizo 9050s monitor (similar in features to the one mentioned in This answer), which has a "color switch" in the front, with the settings "green/color/amber". In "green", the signal to the red and blue guns is completely shut off. In the "amber" position, the signal to the blue is shut off, and the one to the green gun is approximately cut in half (without modern stuff like "gamma correction"). This switch is at the output of the color decoder, so it works both with analog and digital signals, and all kinds of supported digital signals.

I built myself an MDA input cable that wires all of R/G/B to the MDA "video" pin and "I" to the MDA "intensity" pin. This allows me to get a grayscale picture in "full color" mode, a green picture in "green" mode or an amber picture in "amber" mode. I do not like operating that monitor on MDA, though, because its short-persistence phosphor causes awful flicker on the 50Hz MDA signal, and the same is true for the PAL-timed 50Hz signal generated by my Amstrad CPC computer.

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I suppose it wasn’t that long ago when mono LCD panels were available, certainly by the late ‘80s and you could pick your preferred backlight. I don’t remember a monitor that offered that though.

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    They still are. The ones Mouser stocks (for example) are available with amber, blue, green, yellow, white, or RGB (single arbitrary color) backlights. – Alex Hajnal Mar 25 at 5:53
  • Okay as a theoretical answer. If you can find an actual example, I'll give it an upvote. – DrSheldon Mar 25 at 6:03
  • @AlexHajnal: Do any of those actually take a video signal? They look more like alphanumeric displays. – DrSheldon Mar 25 at 6:07
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    @DrSheldon Yes, these are full graphical displays. They were used for radar, IFF, etc. A version with three phosphor layers was also used for early color television (with the CBS system's sequential color frame format; RCA's system with color sent simultaneous with intensity ended up winning and became the NTSC standard). – Alex Hajnal Mar 25 at 6:08
  • @DrSheldon Bugger, wrong context. Yes, the modules I linked to are graphical displays (I have one right in front of me on my desk). They're typically addressed over SPI or a parallel system bus but some also accept an analog video signal. Text-only LCD modules are also available. – Alex Hajnal Mar 25 at 6:31

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