On some threads, I see that the time and date stamp is in red. What does this mean? Is it that the OP has read the replies? My Sherlock Holmes hat isn't doing the trick. (I tried searching the boards, but got nothing. Red by itself brings up everything (like preferRED), while "red" gets nothing.)
Just curious ...

A new post will be in bold black. When the post is 24 hours old, the date and time stamp turns red. When it is past 48 hours it turns non bold black. It is a moderation tool so the mods can tell if new posts were added to an old thread. at a glance.

When I was a moderator I used to read every single post on every board I moderated. Any posts in Green, Black or Blue, depending on when we are talking about and which version of TER was in use at the time, I would post on.  

The question the OP asked was about just the date and time stamp turning red, a question which pops up here often. I remember some years back when it was being asked repeatedly and nobody seemed to know, and there were tons of different guesses. DC finally popped in with an answer which he said he learned when he was just "training" to be a moderator, from the TER creator himself. So I assume that is the definitive answer and that is the answer I give every time now. I'm not sure if the current staff mods use that, or even know about it, or if it's just a remnant thing in the software.  

Which makes sense that it would be a different color than the red time stamps.

I have a degree of color blindness, but I can see the difference in the time stamp red and the subject line orange. I'm sure there are slight variations with different computer, tablet, or phone screens too. Anyway, the point was that the subject line color change, and the time stamp color change are two different things.  

You say the subject lines of the posts turn to red after you read them?! That would be really convenient. For me the subject lines are always blue, no matter how many times I read a post or thread. Is this because I'm on a phone? Also, I swear I'm not color blind. I've been tested several times.

If browser history is cleared, the posts you've read won't be orange, but will be blue. And if you use TER from different devices and read a post on one, it won't show as orange on the other devices until you also read it there.

The different devices not crossing over makes perfect sense obviously. But what you said about browser history jarred a thought loose in my feeble brain. It was because I've always been using a private window.  

At least according to my color blind friend.