Abstract AMONG the several arbitrary standards that have been proposed for measuring yolk color, the Heiman-Carver (1935) yolk-color rotor is the one that is most widely used. It has a color scale made up of 24 graduated colors—varying from white through yellow and orange to red—painted on watch glasses. For convenience in referring to the individual colors they are numbered consecutively from 1 to 24. This color rotor is being used in a number of laboratories throughout the country and has seemed to be the most satisfactory standard so far devised. Unfortunately it lacks the two most essential characteristics of a satisfactory color standard; that is, permanence and reproducibility of the individual colors. Although this lack of permanence of the individual colors impairs the value of the rotor, it could be used as a color standard if, when fading occurs, the original color scale could be reproduced. However, the difficulties . . .