This is a new problem, just started happening in the last day or two. Thread titles should be in non-bold text once I’ve clicked on them during a session, until they get a new post, but that doesn’t happen anymore. They remain bold, and it’s much harder to keep track of which threads I’ve already read today. 
*** Ponder
I found this thread by googling /straight dope thread title bold/, and have no idea where else to look for an answer. My thread titles come in three forms: gray, blue, blue-bold. It seems to be random. Is there an explanation somewhere of what this code signifies? Answer not urgently needed.
it isn’t random.
the bold blue is threads unread by you.
the thin blue is threads unread by you but there are old postings in.
the bold grey is threads that you have read but there are new postings in.
the thin grey is threads that you have read but there are old postings in.