XF 1.5 What determines which node-sprite conversation bubble displays? What do they mean?

[tribedude]

I am wondering what the lighter and darker colored node-sprite conversation bubbles mean? I thought it meant that you have read a forum (2) (or not (1)), but i have read threads in a few forums and the icons haven't changed....

Maybe I get their meaning wrong here...

 

[Brogan]

Unread posts, no unread posts.