Recently, several new Calibrachoa La Llave & Lexarza (Solanaceae Juss.) cultivars have been developed with novel red and blue flowers. Most wild species of Calibrachoa have purple flowers. The differences in color were not due to anthocyanin composition, but rather to vacuolar pH. The pH of the red-flowered cultivar was 4.8 while that of the blue-flowered cultivar was 5.6. The wild purple-flowered species had an intermediate pH of 5.0. These data suggest that different pH and pigment genes may be introgressed into other Calibrachoa species to increase cultivar diversity.