mark, the post id info turns red and stays red until the 48 hour mark, at which time, it turns black, but not a bold black like the posts less than 24 hours old. So:
Post Age Color of ID tag 0-24 hrs. Bold Black 24-48 hrs. Red 48 and after Black
There were a few reasons to code the site like this, but the main was as a Mod tool. A mod could quickly look at the thread and see if there were any new posts mixed in with the ones from the previous day as they would be bold black in a sea of red. This was kind of outdated by the changes to the mod menu in 2009.
The 48 hr mark was picked because the threads were considered stale and were usually on the 2nd page and beyond after two days.
The founder actually explained this to me when I was training to be a mod, so it is not a theory.
567 times that question was asked. LOL. Even the other mods couldn't answer. Others have come up with possible answers, but every theory was proven wrong. I think the last time that question came up about a month ago, someone did come up with what you just said. But as you said your answer is not theory.
is to show which responses belong to which posts. In a long thread, when looking a post at the bottom, it can be hard to tell if the response was to the OP or to the first comment. Unless you look at the color and shape of the bullet point.