An idea.

When a new post is made the icon to the left side of that forum section changes from that greyish tint to a manilla folder kind of colour (is that colour called Manilla? honest, don't know:-) ). Would it be possible (or even worthwhile) having the system change to a third colour to denote that new posts have been made in a number of different topics?

ie,

Grey.... no new posts
Manilla folder kind of colour, new post in one topic
Red (or something), new posts in two or more topics

Thoughts?