JARS v46n2 - Errors Found in R.H.S. Colour Chart

Errors Found in R.H.S. Colour Chart
Donald H. Voss
Vienna, Virginia

The following will be of interest to those of our members who use the R. H. S. Colour Chart , together with the ISCC-NBS color names in the Huse & Kelly pamphlet published in 1984 by the American Rhododendron Society ( A Contribution Toward the Standardization of Color Names in Horticulture ). Mai Clark has called my attention to a discrepancy: the color name associated with color chip RHS(66) 19B does not make sense in relation to the colors and names of adjacent chips.

The CIE x,y,Y coordinates for chip 19B as published by the Royal Horticultural Society (R.H.S.) in a pamphlet accompanying the color chart appear to be wrong. Repeated measurements with a colorimeter have yielded results placing 19B in the ISCC-NBS color-name block "light Yellow." Conversion by formula of the RHS-published coordinatees into Munsell notation give a result differing by only 0.1 chroma step from the notation derived by the National Bureau of Standards' computer program and published by Huse & Kelly.

Thus, the name "light yellowish Pink" published for 19B by Huse & Kelly is a correct translation of the coordinates published by R. H. S. - but an erroneous name for 19B! Additional evidence of the error appears when the x,y,Y coordinates are translated into the CIE-LAB system. One measure, called hue-angle, arrays the hues (red, orange, yellow, green, etc.) around a circle and associates them with angles from 0 to 360, as on a circular protractor. The colorimeter measurements, which convert to "light Yellow" show a difference of only 2 degrees in hue-angle between the 19A and 19B chips. But the data published by R. H. S. in 1966 imply a (clearly erroneous) hue-angle difference of 15 degrees toward red.

The methods employed above will be used to examine the other chips and their ISCC-NBS names as published by Huse & Kelly. If additional discrepancies are found, I will seek to convey them to fellow members.