On the 'Home' page on the forums, if you scroll down there will be different server specific parts of the forums. Why is the 'Parkour' one a dirt block instead of a grass block? I thought that the old forums was a dirt block .. does that mean that you can't post anything on Parkour right now, or is my guess not correct (because I didn't try )? ---->
The dirt block means that it is the old parkour forums. The grass block... means that it is the current parkour forums, and yes you can't post anything in the old forum sections that have a dirt block. If they have a grass block then yes you can. By that I mean like old parkour forums you can't make any threads or replies. Current parkour forums you can make threads and replies.
The Grass Block indicates that there are messages within that sub-forum that you have not read. If you see a dirt block, then it means there are no new messages within that sub-forum that you have not already read. next time someone posts something in that sub-forum, the dirt block will become a grass block again. Edit: you can still post inside the parkour sub-forum.