>>45,46
I tracked down an archive of the thread I read about the board in from a couple of years ago. The name of the board was not mentioned in the post, and the image was excluded from the archive, but the name was included in the filename of the unarchived image. From that I was able to search and find an archive of the image and the source repository:
https://i.warosu.org/data/g/img/0472/37/1427751389873.png
https://github.com/nkeronkow/tolxanka
So this is actually a novel imageboard engine called Tolxanka. The first color coded column indicates the current post, the second the parent post. My understanding is that the diamond on the far right is used to narrow to a post as if it were the root (OP) of a thread hiding all other posts in the original larger thread. Further of interest is that threads are organized by tags rather than boards similar to a bouru style imageboard, and it's a real-time board (which I've honestly not heard great things about).
Most people will not handle 10+ color coded subthread categories in memory.
I think you're completely correct, and I think the author of Tolxanka would have agreed. The impression I get from the screenshot is that these colors are pleasant to use as a reference system (not storing the colors in memory but more like one would read an indented thread, looking up the post at an indentation level lazily) when they are relatively local, and less so otherwise. This is likely why the narrowing functionality was included, and I could see it being rather adept at this; unfortunately, there is no active instance or archive so I can't really test this. I might put up a private instance for a few friends to test the ideas at some point.
