I think so - opening a post automatically "refreshes"... Mimi?
At least I think so.
I "worry" (well...) about skimming over the unread posts, deciding I don't want to open them up (so they stay red), then having brand-new posts (since I logged on) them get lost in the shuffle when I hit "mark read".
I think everytime you go back to the "main page" it refreshes. So if you are caught in between reading one post and returning to the main page, the new posts (since you have been into that new post) would appear the color red. So be careful about hitting the "mark read" command, because it will turn everything grey, whether or not you have actually read it or not. I think.
Hitting "refresh" would just do what I said above, if I am wrong and it doesn't automatically refresh when you go back to home. I don't refresh before moving on from each post, I just do it when I think of it; but yes, you could miss something new if you hit that "mark read" too fast ;o)