Today I wondered what all these coloured icons in the forum are indicating. Here is what I found out.

Announcement is unread
Announcement is unread and locked (reply and editing not possible)
Announcement is read
Announcement is read and locked (reply and editing not possible)

Forum is unread
Forum is unread and locked (reply and editing not possible)
Forum is read
Forum is read and locked (reply and editing not possible)

Topic is unread
Topic is unread and locked (reply and editing not possible)
Topic is read
Topic is read and locked (reply and editing not possible)

That's quite a neat summary qbv8.

I make use of that info each time I come on board. I firstly note the lightblue icon which tells me that there are new comments attached to some thread within that Forum. Those threads are then easily to navigate y their light yellowish colour.

Hint. When coming to the Board for the first time everything is "unread", and obviously you don't want to read everything. It is easy to set the Board as everything having been read so that new material after that point is obvious. At the top of the Board Index is the link phrase Mark forums read and everything is done automatically.

I usually maintain a tab for "View Unread Posts", refresh it when the urge is on me, then read from the last post at the bottom of the list upwards and refresh again to make sure nothing has been added since I started reading. Then I get on with something else of interest before refreshing the tab again during a spare moment.