All fire department vehicles in service shall be identified by red lights of an intermittent flashing type, visible from both front and rear for a distance of 500 feet under normal atmospheric conditions. Such red flashing lights shall be well separated from the headlights so that they will not black out when headlights are on. Such red flashing lights shall be in operation at all times when such vehicle is on emergency status. Fire department vehicles may also operate rear-facing blue lights. The combination of red and blue lights shall only be used at the scene of the emergency.