An Iris message is a type of video message that is used by gods and demigods to communicate with others using a rainbow.The service is managed by the Greek goddess of the rainbow, Iris .
To send a message, one must first find or create a rainbow with mist and then throw a golden drachma or anything with a good price into it, saying or thinking very deeply:
"Oh Iris, goddess of the Rainbow, please accept my offering."
In The Son of Neptune, when they meet Iris, she tells them that the cloud nymph Fleecy will send an Iris message for them. Fleecy gives them a "direct line" with the saying:
"Oh Fleecy, do me a solid. Show (name and place of person)."
This is usually said aloud, though it works non-verbally as well. Then the caller says the name or location of the intended recipient. The way to end an Iris message is to wave one's hand through the mist, disconnecting the signal.
Iris messages can also be sent to gods, such as when Percy contacted Mr. D. This is odd, because in The Titan's Curse, Percy wonders if it is even possible.