During a preflight check, what color should the humidity indicator on the PBE be?

The correct answer is that the humidity indicator on the PBE (Protective Breathing Equipment) should be blue during a preflight check. This blue color indicates that the PBE system is in a proper condition to be used and that it is free from moisture, which can affect its functionality. If the humidity indicator shows a different color, such as red or yellow, it signifies that the equipment may not be operational or is compromised in some way, and it should not be used for safety reasons. Proper preflight checks are crucial to ensure that all emergency equipment is functioning correctly and is ready for use if needed during flight.