A series of important modern color order systems are examined. These include the Munsell system, the Optical Society of America-Uniform Color Scales (OSA-UCS) system, the Natural Color System (NCS), the Deutsche Industrie Normung (DIN) system, the Coloroid system and the Ostwald system. The history and principles of each system are summarized. The relationship between these color order systems and the Commission Internationale de l'Éclairage (CIE) system is described. Some of the interrelationships between systems are considered. Finally, the possibility of an internationally recognized color order system is mentioned. -- AATA