The reason why female flight attendants wear red lipstick is so that passengers on the plane can read their lips during an emergency.
It makes the female flight attendants lips more visble to make it easier to read their lips should they not hear the flight attendant.
During training, flight attendants are instructed to wear lipstick "so passengers can read their lips during an emergency".
When attending a flight attendant interview it may help to have a natural look with mascara, eyeliner and natural color eyeshadow with red or pink lips.
You can look online for flight attendant photos to help you choose an appropriate look.
Female flight attendants are known for their flawless make-up, even after several hours on their feet during long-haul flights when everyone else looks at their worst.
It turns out, part of their perfect beauty routine is actually for a serious reason - passenger safety.