The Myth of Iris from "Flower Lore and Legend"

In ancient myth, Iris, the sister of the harpies and goddess of the storm, was represented by the rainbow. She was as swift as the wind, had wings of gold, and was employed by Juno for her especial messenger, as Mercury was the messenger of Jupiter. She carried messages unto the ends of the earth and even into the depths of the sea. By some of the Greek poets she is called a virgin goddess. One day the flowers all assembled at the invitation of Juno to celebrate the birthday of Iris. They all came in their prettiest dresses and were having a fine time when three new sister flowers were seen approaching, dressed in gowns of red, yellow, and purple, and wearing gorgeous jewels, but no one knew who they were. As they were without names, they were christened Iris, because they wore the colors of the rainbow, and thus it is that they bear the name of the messenger of the gods.
~K.M. Beals, Flower Lore and Legend