Construction and use of a multi-shelled gamut boundary descriptor for an RGB display device in which one shell is an outer “plausible” shell and another shell is an inner “reference” shell. The outer shell is coterminous with a unit RGB cube. The inner shell is constructed based on eight reference primaries in the RGB cube, corresponding to primary colors black, blue, green, cyan. red, magenta, yellow and white. Both the inner cube and the outer cube in RGB color space are transformed to a perceptual color space, thereby defining the GBDs for an inner and an outer shell of a multi-shelled GBD.