I am using the pro-bw scheme and when there is a new post, the icon is red. If it is a thread I have posted to, it has a star in it. What the other schemes present as I am not sure, but yes there should be a difference. In the pro-silver that I started with, I also had difficulty, but it was different. I think you can also click the view new posts link at the top of the page to view posts you haven't looked at yet.
Hope that helps and leaves you less confused than I am now..