@izaya (This is from a emergency responder view, in germany. The actuall codes might be different depending on where you are.)

@izaya "to code" is used in the medical field to indicate a patient is entering a critical state, e.g. cardiac arrest.
Patients are often classified by the severity of their injury, so a person with "green" is injured but not in critical, and will also not be critical if not treated for some hours, "yellow" is not imeadiatly critical, but will be serius danger if not treated soon, and "red" is in a critical state, and wil either suffer lasting consequences or die if not treated imeadialty.