Scented flowers depend on bees for pollination and survival of the species. Unlike birds and bats, bees can smell the fragrance of flowers and then see the flowers when they get closer. Apple trees, cherry trees and most fruit trees have a sweet scent that attracts the bees to pollinate them.
Blue or purple flowers like pansies are another one of the types of flowers bees look for. They are usually irregularly shaped and have a landing platform. The flower is often slightly scented and has a narrow floral tube, small enough to fit the tongue of the bee.
Yellow flowers are attractive to bees if they, like the other colored flowers, have a landing spot. The snapdragon is a good example of a flower evolved to exist with bees. The weight of the bee on the lip of the flower opens the blossom to reveal the pollen inside.
Since bees see better at the lower end of the ultraviolet spectrum, they see ultraviolet as an actual color. Some yellow or blue flowers also contain ultraviolet markings that attract bees specifically more than other pollinators do. Some flowers like the buttercup (Ranunculus) look yellow to humans but to bees, the centers are dark, forming a bull's eye effect. Although bees cannot see red flowers, they can see ultraviolet markings within some red flowers like poppies.