What color is NOT used for pickup zone marking according to the established guidelines?

In the context of marking pickup zones for helicopter operations, color coding plays a crucial role in ensuring clarity and safety for pilots. According to established guidelines, certain colors are designated for specific purposes.

Green is used for marking pickup zones indicating that the area is clear and safe for landing. Blue is utilized for medical evacuation (MEDEVAC) zones, helping distinguish these critical areas from others. Yellow may denote multiple purposes, often signaling hazards or caution zones.

Red, however, is not employed for marking pickup zones. This is primarily because red is conventionally associated with danger or warning signals in aviation contexts. Using red in this scenario could lead to confusion and misinterpretation by pilots, potentially compromising safety during operations. Thus, red is not a color designated for pickup zone marking, making it the correct answer to the question.