What does it mean when a discussion on the forum is grey?

Some of my recent discussion threads have turned grey. And since haven’t had any responses. Does this mean it violated the rules of the forum and were removed? Or is it simply something that happens after some time of inactivity?

I believe they were reasonable and genuine questions and didn’t target any minorities, denomination or group of people. I refrain from using abusive language or threatening rhetoric, I’m just curious. Perhaps someone could shed some light on this? Thank you