Why do some questions show up in a different color box on the screen and some are just white?
You cropped off the answer to your question. Let me explain.
Look over at the sidebar under the heading "Favorite Tags." Those are tags you have marked as your favorites. SE then highlights any question tagged with one of them.
So to answer your question it is because you have modifiers as one of your favorite tags, and SE highlights questions that are tagged with one of your favorites.