The portrait mode black and white layout of this is similar to the high resolution black and white displays which were in use with some more expensive Mac based "desktop publishing" setups in the late 1980s and early 1990s.

This was before anyone could reasonably afford a 20" full color monitor, and it also would have been too expensive or I/O intensive on the video expansion card to be capable of driving a 1280x1024+ monitor at 256 colors or better. I think also something related to being a crisper image with early 1990s tech level of CRT monitor re: dot pitch if the image was entirely black and white?

For instance:

https://www.reddit.com/r/retrocomputing/comments/1oim0m6/hol...

https://www.reddit.com/r/retrobattlestations/comments/707q70...