The research reported in this dissertation encompassed the investigation of the sources of variation in visual judgment of color differences in textiles and the consequent disparities in color differences calculated from instrumental color measurement. In a paired comparison method, 46 color pairs, including color inconstant samples, were assessed four times by a panel of 59 observers under two daylight simulators, filtered tungsten and F7. Observer variation was assessed with performance factor analysis for observer accuracy and repeatability and by Kappa statistics for observer reliability. Accuracy and repeatability were low compared to previous studies and assessment of inter- and intra-observer reliability showed poor agreement in visual judgments within and between observers. While observers were found to be the most significant source of variation, observer accuracy and repeatability were significantly higher for samples viewed under the filtered tungsten simulator, as compared to F7, leading to the conclusion that choice of simulator affects visual judgments. Visual results were also used to test the effectiveness of four color difference formulae: CIELAB, CMC, CIE94, and CIEDE2000. Using performance factor analysis with confidence intervals formed with a bootstrap method, instead of the simple ranking that has been used in other research, no statistical difference was found in the performance of any color difference formula for either simulator. However, the combination of CIEDE2000 and filtered tungsten consistently showed less variation. The use of constant and inconstant samples did not affect the results; however, the effect may be due to the large color differences of the inconstant samples. Even though prediction of visual judgments by color difference equations was low, the importance of instrumental color difference evaluation is supported by its stability in contrast to the variability demonstrated by observers.
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