I've been trying to figure it out but I give up. I don't know what a highlighted question on JLU means. They're highlighted in light-blue on my computer, and highlighted light-yellow on my android phone. What does it indicate?
It means that a question has a tag that's in your "favorite tags." If you don't have any favorite tags, the software picks the tag you're most active in, and highlights questions with those tags.
It confused me too, the first time the random highlighting showed up. You can get it to go away by adding one tag to your favorite or ignored tags--I added a rare tag to my ignored tags, and voila! No more weird highlighting.