1. Munsell Book of Color, Munsell Color; 1980. GretagMacbeth, New Windsor, 1980.
2. Atlas normacolor spatial system. Mecanorma; Le Perray-en-Yve Pines, France, 1990.
3. NCS—Natural Color System: A Swedish Standard for Color Notation
4. NCS, natural color system?From concept to research and applications. Part I
5. CIE Supplement No 2 to Publ. 15, Recommendations on uniform color spaces, colour difference equations, and psychometric terms (1978).