This study investigated bract color phenotypes and pigment composition in Bougainvillea × buttiana ‘Mrs. Butt’ and six bud-sport varieties at the full-bloom stage. Bract color was evaluated using the Royal Horticultural Society Colour Chart and CIELAB parameters, whereas pigment classes and contents were determined using qualitative color reactions, UV–Vis spectroscopy, and spectrophotometric assays. Data were analyzed using one-way ANOVA, Duncan’s multiple range test, Pearson correlation analysis, cluster analysis, and pigment ratio analysis. The seven varieties were classified into red/pink and orange/yellow groups, which differed significantly in L*, a*, b*, C*, and H°. Betalains and flavonoids appeared to be the predominant pigment classes, whereas chlorophylls and carotenoids were present at relatively low levels; no characteristic anthocyanin absorption peak was detected under the present UV–Vis conditions. The betaxanthin/betacyanin ratio was positively correlated with L* and b* and negatively correlated with a*, suggesting that this ratio is associated with variation from red-dominant to yellow-dominant bract coloration. These findings suggest that bract color variation in this bud-sport lineage is associated with the combined effects of betalains and flavonoids, and that the betaxanthin/betacyanin ratio could serve as a practical indicator for color classification and low-cost assisted selection in Bougainvillea.