T'Challa and Nebula
Nebula noticed the man in the red suit - he was impossible to miss - and the guards who were doing their best not to be noticed. She was used to being able to assess a scene and establish the threat level very quickly. If she hadn't learned that skill very early in her years with Thanos, she would have been killed a long time ago.
As she approached, she nodded to the guards, acknowledging their presence. All they would see was who their king would see: a red-haired woman wearing jeans, a red plaid shirt and Converse. As a threat, she probably didn't register.
Nebula paused a few feet from T'Challa and gave a shallow bow. It seemed appropriate. "Good Afternoon, Your Majesty." Would he recognize her as the woman who had jumped on a creature during the Plum Island attack? She didn't know.