Maybe this should be posted in technical?

But I am curious -- The area to the right of post title there is a bunch of information in twolines. On the top line is who last replied and how long ago, and the number of replies, side by side

Then under that is the heart and the camera icon.

I have noticed that when I open a thread all that stuff changes colour. (From green to grey.)

But I have noticed something else, too, and it is puzzling me. Sometimes the number of comments has a grey box around it (or a green box as the case may be)--and sometimes it doesn't.

Why?
What does it mean?