Are you perhaps referring to the fact that the background colour is different for new/unread posts?
If so, then that's done via your .css stylesheets.
Perhaps the old version you speak of uses different classes than the latest one does, and thus not everything is being read correctly. Perhaps they are specific to certain versions, that would be my guess.
Since I don't have an example stylesheet for such an old version, I cannot help you more on this question :-)
Perhaps someone else can.
