The Chroma Pro was a series of screens introduced after 1985. I remember using a CM 2000 in the late 80s.
RGBI is essentially IBM CGA.
RGB is Analogue RGB.
I used both modes with IBM and an Atari ST.
XRGB in turn should be what Apple used to call the Apple III's digital video signal. It's a 4 bit TTL compatible digital port. See this pinout). The Extended 80-...
From my reading of that post linked above, XRGB is a variation of RGB that maps to NTSC artifact colors, rather than the usual 16 seen with RGBI. This is likely related to the Apple 2 and IBM CGA 16 color artifact palette and monitor suitability for software written with artifact color in mind.