Modernization of Physical Appearance and Solution Color Tests Using Quantitative Tristimulus Colorimetry: Advantages, Harmonization, and Validation Strategies  Brian W. Pack, Laura L. Montgomery, Evan M. Hetrick  Journal of Pharmaceutical Sciences  Volume 104, Issue 10, Pages 3299-3313 (October 2015) DOI: 10.1002/jps.24565 Copyright © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association Terms and Conditions

Figure 1 Representation of the CIE L* a* b* three-dimensional color space where a* represents the red-green color axis, b* represents the yellow-blue color axis, and L* represents the lightness axis. Journal of Pharmaceutical Sciences 2015 104, 3299-3313DOI: (10.1002/jps.24565) Copyright © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association Terms and Conditions

Figure 2 Color space coverage by the Ph. Eur., Ch.P., and USP color standards. Journal of Pharmaceutical Sciences 2015 104, 3299-3313DOI: (10.1002/jps.24565) Copyright © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association Terms and Conditions

Figure 3 Metamerism exhibited by samples and Ph. Eur. color standards between D65 and F2 illuminants. Squares (Ph. Eur. reference solutions) and capital letters (samples) represent the D65 illuminant, whereas circles (reference solutions) and lowercase letters (samples) represent the F2 illuminant. Arrows indicate movement through a*–b* color space when switching from the D65 illuminant to F2 illuminant. Journal of Pharmaceutical Sciences 2015 104, 3299-3313DOI: (10.1002/jps.24565) Copyright © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association Terms and Conditions

Figure 4 h* (hue) values for all of the pharmacopeial color standards. Top, Ch.P.; middle, Ph. Eur.; bottom, USP. Within designated color “families,” the hue is inconsistent, with the Ch.P. standard illustrating the most consistency within “family.” A horizontal line within each family would indicate consistent hue. Journal of Pharmaceutical Sciences 2015 104, 3299-3313DOI: (10.1002/jps.24565) Copyright © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association Terms and Conditions

Figure 5 Visual descriptions based on color theory applied to all areas of two-dimensional a*–b* color space. Journal of Pharmaceutical Sciences 2015 104, 3299-3313DOI: (10.1002/jps.24565) Copyright © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association Terms and Conditions