The colors of flowers are produced by a variety of pigments. One type is the anthocyanins (= "flower + blue"). This pigment type is water soluble and is found in the fluid filled vacuoles of plant cells. Anthocyanins are typically blue to purple in color and give many flowers their color. This pigment can be found in other plant parts, particularly leaves. The house plant Zebrina and other plants have leaves with the undersides purple. Young leaves of plants are often reddish to purple because the anthocyanins act as a sunscreen shielding the developing tissues from excess light.

Anthocyanins have an interesting behavior that plants make use of in their flowers. The anthocyanin pigment changes color depending on the pH of the fluid in the vacuole. You can notice on many plants, such as Virginia bluebells (Mertensia virginica), that the flowers change color as they open up. The strategy involved is to have the open mature flowers a particular blue color to attract pollinators such as bees. The younger flowers or past mature flowers are a different color. This enhances pollination by making the insect's job easier to zero in on the receptive flowers.