Maerlyn's Rainbow, also known as the Bends o' the Bow or Wizard’s Rainbow, consists of thirteen colored spheres. The first twelve represent the Twelve Guardians of the Beams, each having the secret of a different form of magic; the last, Black Thirteen, represents the Dark Tower itself, which was filled with the evil of the monster-infested void that existed between worlds.
Some have different powers to others with some showing Mid-World, some which show All-World, and some which have the power to transport. Others look into the future and the demon infested worlds as well as revealing the locations of secret doors which give access to other worlds. Additionally, others can see far into the world and witness vile acts most people would wish kept secret. One is said to give the power of levitation, and another the secrets of telepathy.
All were cursed to bring despair and sorrow to those who wielded them, representing a corruption of the White and have a tendency to sap the life of the user, looking into them to a person to see their sins and shameful acts.
They are also referred to as Bends in the Rainbow by Roland's father, Steven. The Bends are referenced at least twice. First, when Roland is talking with his father just before leaving for Mejis and the Outer Arc; second, when the ka-tet are standing in front of the glass gate (in Wizard and Glass), those identified at the glass gate are the Pink, Black, Blue, Green, Orange, Yellow and Purple spheres.
The Thirteen colours consist of: Crimson, Orange, Yellow, Pink, Dark Blue, Dark Green, Indigo, Lime, Azure, Violet, Brown, Pearl Grey, and Black.
It is in The Gunslinger Born that six of these Bends are in the possession of the Crimson King. The only one mentioned by name in the issue is Black 13. The other five appear to be Blue, Lime, Yellow, Orange, and Purple. The Crimson King uses Black 13 to communicate with Walter O'Dim. These events occur around the same time that the Pink Bend is given to the witch, Rhea of the Cöos.
The sorcerer Maerlyn created the objects from the magic of the Prim when Arthur Eld began his rise to power. He created them to bring chaos into the world, and also created demons for every sphere, as seen in the comic The Long Road Home and The Sorcerer. These orbs were given by Maerlyn as a gift to Arthur Eld during his coronation. Once Arthur realized their true evil nature, he ordered them to be shattered, only to discover that they were unbreakable, and so had them hidden away in a cave. Eventually thieves were drawn to the orbs and they made their way back into the world.
The Pink Bend
Also known more commonly as Maerlyn's Grapefruit, it was in the possession of John Farson, and was believed lost by him. However, unbeknownst to him it was taken by the Big Coffin Hunters under the Crimson King's orders to be given to Rhea in Mejis when Roland and friends were sent there. Roland acquired it, and during the return to Gilead he shoots it, causing it to turn into its demon form momentarily, latching onto Roland's soul and taking it into itself where he becomes trapped by the whims of Marten Broadcloak. Sheemie eventually saves him but doesn't return from the sphere. Roland then becomes obsessed with the sphere and starts to waste away, much like Rhea of the Coos does in Wizard and Glass.
People can also become trapped inside the sphere if they touch the orb with blood on their hands.
Randall Flagg, the son of Maerlyn, has a relationship with the demon of the Pink Bend of the Rainbow, whom he calls his sister.
Eventually Roland hands it over to his father Steven and he stores it away. His wife Gabrielle Deschain later steals it and is then killed by Roland as the sphere makes him think she is Rhea as she is livid after discovering Marten has had an affair with her. When Randall learns of what she has done, he forces the demon back into the sphere. The demon also orders the death of Arra Champignon's child.
The crystal can act as a seeing stone showing a single person visions of current and future events elsewhere, presumably only in the same world and show the vilest acts of men. The visions seen can be back-handed, lying through reflection or other tricks to manipulate the viewer towards evil actions. The glass is extremely addictive and can entrance the viewer and cause a severe addiction to being viewed; prime examples of this were Rhea, and later Roland as well.
The Black Bend (Black Thirteen)
We first see the sphere in The Gunslinger Born as Marten Broadcloak contacts the Crimson King in Le Casse Roi Russe through it. The Crimson King used it to monitor the events of Mid-World and to communicate with his agents.
"Black Thirteen" was given to Father Callahan by the man in black while
Roland was chasing him. Callahan was transported to Calla Bryn Sturgis by it, and subsequently hid it away after settling down in the Calla. When Roland's ka-tet arrived in Wolves of the Calla, he offers it to Roland as incentive for their aid.
Mia steals it after the showdown with the Wolves and uses it to escape to the New York City of 1999, where she planned to give birth to Mordred Deschain. Jake Chambers and Father Callahan follow and retrieve Black Thirteen, then store it in a locker beneath the World Trade Center. The locker is of a sort where the user purchases time at a set rate - Callahan and Chambers purchase enough time to store Black Thirteen well into 2002. The World Trade Center is, of course, destroyed well before the time on the locker runs out. It is not known what precisely happens to Black Thirteen, but the collapse of the towers almost certainly buries it, presumably lost forever.
The Blue Bend was last seen with a band of slow mutants who called themselves "The Total Hogs"; however, they are said to have lost it.
In The Dark Tower VII: The Dark Tower, Rando Thoughtful tells Roland that before killing himself, the Crimson King smashed the rest of the Bends in his possession - presumably so that no one else could have them, or out of thoughtless anger. However it is possible that this is a lie as in The Long Road Home we see the Pink Bend smashed by Roland's bullets but reforms after attacking Roland in its demon form.