You know - you see a title, have a read - decide you have nothing to add to the conversation; it doesn't offend you so you don't hide it
A bit later you see the thread in purple (not blue) & think 'what was that about' so have another look & feel a bit silly
If you could rt click on it & mark it as unread you could just forget about it
I kinda see the purple ones as threads I want to pop into again (iyswim)