Techniques are disclosed for controlling object appearance while maintaining a lighting function without noticeable changes in illumination. The techniques may be implemented to illuminate a given target with a first light source so as to cause the target to have a first appearance, and to illuminate the target with a second light source so as to cause the target to have a second appearance different from the first appearance. The first and second light sources have a chromaticity within a common MacAdam ellipse. The MacAdam ellipse size may range, for example, from a 7-step ellipse (for relaxed constancy in chromaticity) to a 1-step ellipse (for high constancy in chromaticity). In some cases, one of the first or second light sources includes a spectral feature not included in the other light source, and an optical response property of the target reacts to changes in the spectral feature thereby causing appearance changes.