1. Method of creating a gamut boundary descriptor of an actual gamut boundary of all colors that can be output by a color device, comprising the-steps of: using an intermediate color device executing: in a transformation color space, selecting gamut boundary colors sampling a surface of said actual gamut boundary, using said selected gamut boundary colors, generating a network of elementary polygons representing said actual gamut boundary, each selected gamut boundary color belonging to an elementary polygon, generating an initial gamut boundary descriptor from said network of elementary polygons, identifying vertices and edges of elementary polygons that belong to a line or a point of discontinuity of said actual gamut boundary, smoothing said initial gamut boundary descriptor into a final gamut boundary descriptor that is closer to said actual gamut boundary than said initial gamut boundary descriptor, wherein said smoothing: does not change position of the identified vertices and of the identified edges, does not change the discontinuities of curvature of said actual gamut boundary at said identified vertices and at said identified edges; and using the fmal gamut boundary descriptor to output an image by the color device.