Wow all 3 gave a different answer.
I think B looks the nicest but it's probably the least obvious what the board is actually about. And between A and C I like the colours in A. It always irks me when the greyscale read forum isn't that different than the unread? Not a deal breaker or anything though.

Honestly if we could hunker down and use the artstyle of B to make original icons for all the forums that could be cool. Maybe like each one a different colour scheme so they kind of make a spectrum

Yeah it seemed a little lofty to begin with