Do you mean a dash indicator light or the ambient lighting itself? Personally, I think that a cockpit with ambient lighting that adjusts based on autopilot status would be a much better indicator. When the autopilot is engaged and everything is copacetic, the lighting in the entire cockpit could be in a dim red color. As the autopilot gets less confident in the situation, the ambient lighting could get more yellow, with an increase in brightness.<p>The autopilot losing enough confidence and wanting to be turned off should blink between two colors and sound an audible alarm until the pilot presses a button to acknowledge the autopilot wants to turn itself off.