Nectar guides are colorful patterns or spots on flower petals that guide a pollinator into the portion of the flower where the nectar can be found. These patterns have evolved over time and aid the plant by assuring adequate pollination by insects, especially bees.
The patterns may or may not be visible to humans. In some flowers, such as sunflowers and black-eyed Susans, the patterns may reflect ultraviolet—a color particularly attractive to bees. Ultraviolet is sometimes called “bee violet” and ultraviolet combined with yellow is known as “bee purple.” If you view these flowers under ultraviolet light, you will be able to see the patterns.