I've been doing some tweaking.
I disabled 'hot topics' so the red envelopes don't show - they depicted a thread of more than 15 replies or 150 views.
So now you have a blue envelope or a grey one. The blue is an open envelope alerting you to a thread with unread messages.
The grey envelope you will notice is closed meaning no unread messages.
The board was set to mark all threads as read after a couple of hours. So if you logged on tonight and looked at threads posted this morning they would all seem to have been read even though you had not even opened them. That setting has changed to 30 days so from now on any threads you have not opened or read will remain unread until you open them or 30 days has passed and it will automatically be marked as unread.
Also this should now mean syncing across devices. If you read a thread on your laptop and then 30 mins later looked at ccmb on your phone the thread would be unread even if no one else had posted in it. Now an unread thread on your laptop is automatically unread when you log onto ccmb on another device.