Oh Paul, that makes my head hurt! HA!! Once a message in a thread has been read, it goes gray.
If I clink on the message's embedded link, it never changes - its always red. When I go to the top and select 'mark all messages as read',then they all turn gray...but the links embedded in each message never change color - they are always red. Why this is different, I don't know.
So...when I go back later to see if there are new postings, I scroll down the page and my eye keeps stopping on all the red embedded links. If new messages (yes, links within a thread) were to be a different color, it would be so much easier to find the new postings.
Am I clear? I've done a bit of HTML so I do understand what you are talking about (mostly). But I guess if I'm the only one with this issue, then it isn't an issue in the grand scheme of things.