Abstract: A color cathode ray tube display apparatus particularly for use under a wide range of ambient light conditions, such as in an aircraft cockpit, wherein each of the primary color phosphors has a unique brightness versus cathode drive characteristic, which characteristic also is dependent upon whether the displayed information is raster written or stroke written and wherein such characteristics also may vary from tube to tube. The output of at least one cockpit ambient light sensor in addition to a pilot selected brightness is used on a continuous basis to calculate a reference brightness level for the sensed ambient brightness conditions and display writing mode, this reference brightness level being used to calculate the corresponding brightness level for each of the primary color components of the commanded symbology color and concomitant drive voltages to the CRT's cathode or cathodes.