Iris was the goddess of Rainbows as well as the "personification of the rainbow in Greek mythology," (greekmythologhy.com)She was also a messenger for the Greek gods alongside Hermes. From what we've found there is no specific myth focusing on Iris. But she does play a pivotal role in several important stories such as in Jason and the Argonauts The Odyssey,The story of Persephone and several others.
Origins of Iris
Iris was born to the Titan Thaumas and the cloud nymph Electra alons with her sisters Arke, Aello, Celaeno and Ocypete. When Zeus and the Olympians fought the Titans, Iris fought with the Olympians while her sister Arke sided with the Titans. During the war her sister had her wings removed by Zeus and gave it to her as a gift. Eventually the wings would end up in Achilles posession on his sandals.
Her limited role in the story of Pershpone
In the story of Persephone, Iris served as a secondary messenger for the gods and was the one to break the news to Demeter that her daughter was in the realm of Hades. Unforutenaly "Demeter did not respond to Iris' entreaty.("httpowlcation.com) After this not much is said about her in the rest of the story.