The goal of this study is to develop quantitative metrics for evaluating color tracking and gray tracking in a color medical display. Color tracking is the chromaticity consistency of the red, green, or blue shades. Gray tracking is the chromaticity consistency of the gray shades. Color tracking and gray tracking are the most important colorimetric responses of a color medical display because they directly indicate the color calibration quality and can therefore be used to compare color performance between displays. Two metrics, primary purity and gray purity, are defined to measure the color shift of the primary shades and gray shades of a color display, respectively. The area under the curves of primary purity and gray purity can then represent the quality of color tracking (C_AUC) and gray tracking (G_AUC), respectively. Fifteen displays including medical, professional-grade, consumer-grade, mobile, and special displays were tested to compare their C_AUC and G_AUC. The OLED displays have the greatest C_AUC values. The medical and professional-grade displays have the greatest combinations of C_AUC and G_AUC values. Most consumer-grade displays have lower C_AUC and G_AUC values, but some show better gray tracking than color tracking. The special displays exhibit particularly poor color and gray tracking. Using C_AUC and G_AUC together can quantitatively predict and compare color performance of different displays.