Flower color is largely due to the accumulation of anthocyanins and/or carotenoids in petals. The vast array of flower colors seen in nature is due to the hundreds of different anthocyanins and carotenoids; variation in the type, concentration, and ratio of these compounds; and the influence of secondary factors such as co-pigments, vacuole acidity, and chelation to metal ions. The availability of transformation protocols for many important cut-flower and flowering pot and bedding plants, in conjunction with the isolation and characterization of the key genes on both the anthocyanin and carotenoid biosynthesis pathways, has led to the development of ornamental species in which flower color has been manipulated using genetic modification technology. To date, only flower color-modified, genetically modified, varieties of carnation and rose have been commercialized. The absence of other flower color-modified species in the marketplace may be explained by the high cost of regulatory approval.