My question has a light gray title, unlike a black title. Why?
Here's the question. You may need to view it on home or on my profile.
EDIT: Ironically, the title on this question is gray. How about that!
It just means that you have visited the question's page previously.
When you visit a link in Ask Ubuntu and that link is part of your browser's history. Any link that is part of your browser's history becomes gray so you can tell that you had previously visited that link.
You can check the following GIF which showcases this behavior. Notice when every time a question is clicked and visited, after going back to the original listing, the text color changes from black to gray for the link I had visited.
This behavior is common on all of the Stack Exchange sites, though colors might differ. In fact, this behavior is common in most of the World Wide Web. For example, Google changes the links from a blue color to a purple color after you visit them.