Artist 
Writer Isochromes
Wilhelm Ostwald’s definition: a term to define colors of apparently uniform hue content (by ‘hue content’ he means saturation) that run in vertical rows about the gray scale.
Faber Birren’s definition: the colors in Birren’s color triangle that run along one of the arcs in which all the colors have the same apparent color content and differ only in value.
Barry John Raybould’s definition. I have created two new terms: mono-isochromes and poly-isochromes in order to be more specific about what is happening to the value of the colors. The reason for the new nomenclature is that I believe that the traditional color wheels used to explain color harmonies are inadequate to explain real color harmony because they ignore saturation and value and only refer to hue.
See the Color Building Block for more information.