Psychology of Colors
Other terrain warning systems generate a color coded map like display of surrounding terrain on an already crowded moving map indicator. The vertical terrain warning system also uses colors to display the straight ahead path of the aircraft.
Very Important......
Different colors tend to blend during periods of stress. Color coded map contours can be completely blocked out by the pilot during periods of severe stress and disorientation. This phenomena, to block out all but the relevant stimuli, is called "Selective Inhibition." The colors tend to blend or have the effect of a psychological "color blindness" while under stress. This is one aspect of other terrain warning systems that have not been addressed. Psychologist have known about "Selective Inhibition" for many years. It is our opinion that the FAA is not aware of "Selective Inhibition."
Motorist have run traffic lights when under stress because they did not see the red light. In other words, pilots under duress may not see the red or yellow colored bands!
Horizontal terrain warning system as
presented on the display.
Horizontal terrain warning system
as perceived by the pilot under stress.

Vertical terrain warning system as
presented on the display.

Vertical terrain warning system
as perceived by the pilot under stress.
While the AMSADD system does enhance the MSA displays with color, there are two fundamental differences between AMSADD and the vertical and horizontal terrain warning systems. First and most important, AMSADD does not allow the aircraft to descend below the MSA, thus the pilot will be kept back from encountering any stressful situation regarding eminent terrain impact. Second, AMSADD uses numbers instead of color coded displays. Since pilots use numbers constantly during flight, i.e., heading, altitude, course, fuel, time, aircraft performance, etc., the MSA is a natural number to compare with the altimeter. "Selective Inhibition" will have little, if any, bearing on a pilot in distress.
When the pilot compares the altimeter to the AMSADD display, altitude awareness confusion is eliminated while under periods of stress or disorientation.

History of Ground Proximity Warning Displays System Comparisons 
 Flight Tests Evolution of AMSADD