Hi there,
I believe if you scroll over it with your mouse, it tells you. I'm on mobile right now so cant check. However I do know what they mean -
Stationary texts on a blue background means it's a thread with no new posts. You've seen all the posts in that thread.
If the lines are moving, it means it's an active topic.
If its red, it means the thread has a post or posts in it that you haven't seen yet.
And if there is a star or an asterisk, it denotes a thread you have posted on.
I'm not exactly sure what makes a topic active or not. Possibly the amount of people who click on it or if its had recent discussion.
Hope that helps
-Brandon