The status quo of flavonoid biosynthesis as it relates to flower color is reviewed together with a success in modifying flower color by genetic engineering. Flavonoids and their colored class compounds, anthocyanins, are major contributors to flower color. Many plant species synthesize limited kinds of flavonoids, and thus exhibit a limited range of flower color. Since genes regulating flavonoid biosynthesis are available, it is possible to alter flower color by overexpressing heterologous genes and/or down regulating endogenous genes. Transgenic carnations and a transgenic rose that accumulate delphinidin as a result of expressing a flavonoid 3',5'-hydroxylase gene and have novel blue hued flowers have been commercialized. Transgenic Nierembergia accumulating pelargonidin, with novel pink flowers, has also been developed. Although it is possible to generate white, yellow, and pink-flowered torenia plants from blue cultivars by genetic engineering, field trial observations indicate difficulty in obtaining stable phenotypes.