quality to which a unique six character

The "quality to which a unique six-character code is assigned, in graphic design," refers to the quality of color represented by the term "hue." Hue is a color attribute that can be represented by a unique code in graphic design systems, often in six-character hexadecimal notation (such as in color codes). The answer commonly given for this is "HUE," a three-letter term representing the dominant wavelength which defines color quality.