In the proposed modified opponent-colors system, the hue regular rectangles show the chromatic coordinates of any, chromatic colors better than hue circles. In the hue rectangles equihue and equichroma loci are shown together with equigrayness loci. In the color perception space of the modified opponent-colors system, a city-block metric must be used instead of a Euclidean one for distance. The reason for this is described in detail. The proposed color perception space constitutes a regular octahedron.