I was wondering if there is anything available to change the images for each of the subforums. I see this forum does it (the nuclear sign for the first subforum, ...).

One thing I don't see here is that it doesn't make it gray when all threads in a subforum are read (like the original vBulletin style does).

I think you are refering to the status icons (new posts, no new posts made in the forum). From my understanding you have to replace the stock images with your own (usually a color one, and the other a dark one).