What color indicates the maximum operational limit on an airspeed indicator?

The color that indicates the maximum operational limit on an airspeed indicator is red. This color signifies the absolute maximum speed that an aircraft should not exceed in order to maintain safe operation. Exceeding this limit can lead to detrimental consequences for the aircraft, including structural failure or loss of control.

The other colors on the airspeed indicator serve different purposes. Green indicates normal operating range, meaning the aircraft is within safe speed limits for routine flight operations. Yellow represents caution and is generally associated with operating speeds that are not recommended for most conditions, indicating a need for careful operation in that range. Blue is used to denote the best rate of climb speed, where the aircraft can gain altitude most efficiently. Understanding these colors and their corresponding meanings is crucial for pilots to ensure safe flying practices.