nah, that's just the monitor... CGA was mono on a mono monitor but otherwise it was ugly black, cyan, red and i forget what colour, blue maybe, been quite some time since i saw CGA... CGA was the beginning of the adoption of color monitors, so many people first saw it on mono 

 https://upload.wikimedia.org/wikipedia/en/2/2a/Alleycat.png

yeah, it was literally CMYK (magenta, cyan, yellow, black) 

 ok, white, magenta, cyan, black...

some more examples of this typical CGA display from those days (late 80s) https://www.mobygames.com/game/16195/galactic-conqueror/screenshots/dos/1064275/ 

 My monitor was definitely capable of RGB. Windows 3.1.1 worked, full color in MS Paint, etc.

This was like 25+ years ago, so I don’t remember the details. Just that when I tried to play it in full color it was garbled and choppy. Monochrome worked though. 

 oh, CGA also had the original mono mode with twice the horizontal resolution, i forget what the original mono mode was called 

 and yes, it literally would have been one pixel on one pixel off ind opposite order for the purple and cyan, i remember this... 

 nah, that's just the monitor... CGA was mono on a mono monitor but otherwise it was ugly black, cyan, red and i forget what colour, blue maybe, been quite some time since i saw CGA... CGA was the beginning of the adoption of color monitors, so many people first saw it on mono nostr.fmt.wiz.biz 

 7th guest was cool, though I had to cheat to solve a lot of the puzzles (I was quite young). Not sure if I ever got around to trying sequel. Shyly spryly...