Old post, I know, but I thought I could shed some light. That guy is a plane captain. I was also a qualified plane captain, as are most other sailors in the Naval aviation community. He's wearing yellow because he's qualified to perform that task on the boat, which isn't always the case for all plane captains. The plane captain is an enlisted service person who did the required training to perform that function, which includes inspections, signaling, training others and other ground operations. While anyone from a Chief, on down to an E-1 Airman can train to perform the task, it's usually a Third Class (E4) or a Second Class (E5) Petty Officer. The sailor has put the markings on the cranial as flair, so that it can be quickly identified among dozens of others. The blue is blue because that blue 'painters tape' is everywhere, all the time, because our airframers use it when they paint. It's common to see it on cranials. The white square is painted directly onto the cranial sometime before they're put into service.

Edit: I read another sailor's comment here. We never had numbers on our cranials, but that sounds totally reasonable. Our sailors just put some distinct marking on them. Policies change fast, though, and they can be different between commands.