In general, flower color is due to two different pigments - flavonoids, and carotenoids. These pigments are responsible for yellow through orange colors.
Flower color is the result of mixing the two pigments in different proportions.
By mixing and matching these pigments, a wide array of different colors can be created. For example, the red color of in several plants is the result of mixing orange carotenoids with magenta flavonoids. Most flowers do not contain carotenoid pigments. The only pigments present are flavonoids. The addition of co-pigments to the anthocyanins increases both the stability and intensity of the anthocyanin's color.