How is a failed NAV radio indicated on the MFD display?

The correct choice is significant because it highlights how the multifunction display (MFD) communicates the status of the Navigation (NAV) radio. When a NAV radio fails, the frequency displayed changes color to amber instead of the normal green. This visual cue is crucial for pilots, as it signifies that there is an issue that needs immediate attention, distinguishing it from successful operations or normal indications.

Using amber as a warning color effectively communicates caution without being as severe as red, which typically indicates a critical failure or outright malfunction. This color coding is an essential aspect of visual indication on avionics displays, helping pilots quickly recognize and respond to system statuses during flight operations.