Pollination
Many species of flowering plants are dependent on another individuals— insects, birds, or bats—to achieve reproduction. Simply by walking outside we can observe that there are many different characteristics of flowers from color to structure, that have evolved to attract a specific type of pollinator. This page is here to explain this vast diversity of these flower traits! Keep in mind that there are other organisms that are pollinators but these are main ones I've decided to cover.
Birds
Ipomipsis aggregata
Image by CalPhotos
Hummingbird feeding on nectar
Birds are attracted to red and purple flowers because they see well in that light spectrum. Flowers that are pollinated by birds contain sugar rich nectar as a food source/reward for the pollinator. Ipomopsis aggregata seen on the right is pollinated solely by hummingbirds who have a long enough beak and tongue to reach the nectar located at the bottom of the long corolla. Also unlike other flowers, bird pollinated flowers do not emit any odor, it is unnecessary because birds do not have a sense of smell.
bees
Honeybee feeding on pollen
Image by My Little Green Foot
Bumblebee covered in pollen grains
Image by National Geographic
Bees are attracted to flowers that are yellow or blue, either on the petals themselves or towards the inside of the flower. The yellow is like a bright flashing light to them indicating where pollen is, which is their food source. Bees feed on both pollen and nectar. They are not the most agile creatures so they benefit from the flowers large and sturdy landing pad-esque petals that can support their body weight.
Moths and Bats
Darwin's Orchid
Image by GrowerCoach.com
Bats and moths are mainly attracted to white flowers that have a strong scent. Since these two pollinators are nocturnal being able to smell your food source, in this case nectar, is very helpful. The flower pictured in the middle is called Darwin's orchid because it was believed that there could not possibly be an organism that had evolved in order to reach the nectar at the bottom of the corolla and Darwin had discovered a moth with a tongue that perfectly fit the length of the corolla of this orchid.
Flies
Image by Tatyana Soto
Flies are often thought of as pests but rarely thought of as necessary pollinators for many species of plants. Flies are unique pollinators because they are not searching for a food source, rather they are looking for a place to lay their eggs. These species typically have dark red/purple petals and emit a putrid odor that mimic decaying meat which flies have an affinity to and view as a food source for their offspring once they hatch. One of the most famous fly pollinated species is Amorphophallus titanum, commonly known as the corpse flower, because it is the largest flower in the world and only blooms every seven years. I had the lucky chance of smelling a blooming corpse flower (middle) at the Conservatory of Flowers in San Francisco whose smell lives up to its name.
Butterflies
The last stop on this list of pollinators is the butterfly! Butterflies are attracted to brightly colored flowers and those that large enough to support their body weight. Again similar to moths and hummingbirds, butterflies use their tongues to access nectar inside the flower. While they are attracted to the same bright colors that bees are attracted to, their ability to see red allows them to identify other flowers as a potential food source without having to compete with bees for it.