i have an article on "color discs used in soil color analysis" from science, LXVII no. 1739 (april 27, 1928) by GB Bodman -
he describes "munsell rotating color discs" which "are made to rotate upon a motor-driven shaft, and prvide a means of matching a very great number of colors simply by altering the relative proportions of the different color discs exposed to the eye"
anybody ever seen one of these things?