I'm sorry - I can't tell when I've already read responses to my posts? I see underlines, bolded text, numbers on the left, purple v. blue font. How can I tell which post responses I've already read / not read?
1. If a post has unread (unmarked) replies on your 'My Posts' page...
... there should be a yellow arrow to the left of the post title. When you click on that arrow, it should expand the table to list the replies to your post - anything with a yellow page is newer than the last time you clicked the 'Mark as read' button.
Yellow indicates new replies (just like the 'My Posts' tab lights up yellow to indicate replies since the last time you viewed your 'My Posts' page). When you are done reading/replying to new responses, click the 'Mark as read' button to change the icon colors to white (read). Any replies made to you after you click the 'Mark as read' button will show up in yellow the next time you visit your 'My Posts' page.
At least that is the way the function built-in to the DU3 software works to allow you to track new posts. If you access DU from different computers/devices, it is probably the only way to keep things in sync. For people that always use the same computer, you could probably also keep track by noting which links to replies were marked as visited by your browser (usually purple vs blue for visited vs unvisited links).
I believe bolded text indicates opening posts on the 'My Posts' page.