Measurement of surface color and color difference of tablet colorants by tristimulus colorimetry

The surface color of a series of color dispersions containing from one to three FD&C or D&C dyes suspended in a sucrose syrup was examined using tristimulus colorimetry. CIE (x, y) and Hunter (a, b) chromaticity data, determined directly from an integrating sphere colorimeter or from reflectance spectra and suitable calculations, were used to order materials by color on expanded chromaticity diagrams. Color difference was evaluated quantitatively from Hunter (a, b) data using the Judd color difference formula. Quality control specifications were established either by defining areas of acceptable color by applying limits to the chromaticity coordinates of color standards or by requiring the Judd color difference to be less than a specific number of National Bureau of Standards standard units. This method eliminates the subjective character of color evaluation and permits the quantitation of visual color difference. These differences can be used, in conjunction with defined color standards, to develop color specifications for tablet colorants, finished tablets, and liquid and cream pharmaceutical preparations.