However, there must be more to the story, because often I will visit the Mudcat main (recent threads) page and find that ALL the links have reverted, including those for threads with no new messages. The link URLs themselves ought to be exactly the same (same base URL with the same argument [number of messages now in the thread]), and the only change I may have made to viewing the page has been to change the viewing age (I typically start viewing the main page specifying the cutoff age as two days rather than the default one). I just did a test changing the age, though, and my links hadn't reverted. Curiouser and curiouser.

The link colors will also revert if you clear your browser's "history".

Link history is specific to your browser, so typically, if you change browsers, expect your link colors to revert accordingly.