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...