The first, flavonoids, are quite common in roses. They produce red through blue colors. Carotenoids, found in sunflowers and marigolds, produce yellow and orange coloring. Chlorophyll, the third pigment, gives plants their green color.

Each of these pigments is stored in special compartments in the flowers' cells. Flavonoids, for example, are located in water-storage areas of the cells called vacuoles.

A change in the acidity level of a cell or soil, for that matter, can trigger pigment color changes in certain flowers like petunias and morning glories. Catch this last flower early in the morning, and you'll notice that its buds are bright pink. But in the afternoon, after they've opened, the petals are a pale blue.