"Maerlyn's Rainbow" A.K.A. "The Bends O' the Bow"
The Man in Black's father, the demon sorcerer Maerlyn, created the spheres from the magic of the Prim back when Arthur Eld began his rise to power to be a trick coronation present for the newly crowned King of All-World. He created them to bring chaos into the world, and also created demons for each sphere. Each bend has its' own specific magical speciality; as well as a specific curse inflicted upon the forces of the White whenever they use the spheres.
There are 13 spheres, each of them representing one of the Guardians of the Beams - except for the 13th black sphere, which represents the Dark Tower itself.
NOTE: None of this is affiliated with The Dark Tower or any other of Stephen King's works. It is NOT meant to be canonically accurate. I simply used what information has been made available via the canon material, leaving the rest to be put together as I saw fit. I did so using my own occult knowledge of magical correspondences in logical ways into something that makes sense to me. Again, this is NOT meant to be canonically accurate!
BLACK SPHERE (A.K.A. "BLACK 13") : Beam Guardian = N/A (Represents the Dark Tower)
Red Uses : Communication. Transportation between all worlds. Shape-shifting. Levitation. Illusions. Magical amplifier.
White Curse : Corruption/Insanity.
PINK SPHERE (A.K.A. "MAERLYN'S GRAPEFRUIT") : Beam Guardian = Horse
Red Uses : Current/Future visions of the world that it is occupying at the time. Reveals a person's most vile acts.
White Curse : Obsession/Wasting/Lust.
YELLOW BEND : Beam Guardian = Fish
Red Uses : Domination over others. Divination of all worlds.
White Curse : Paranoia/Cowardice.
VIOLET SPHERE : Beam Guardian = Eagle
Red Uses : Seeing into the future. Prophecy.
White Curse : Physical blindness.
DARK BLUE SPHERE : Beam Guardian = Wolf
Red Uses : Telepathy
White Curse : Auditory hallucinations.
CRIMSON SPHERE : Beam Guardian = Bat
Red Uses : Spirit Communication. Necromancy. Deciphering ka-tet lines/fate.
White Curse : Wasting away physically & magically (if the wielder has any magical abilities).
ORANGE SPHERE : Beam Guardian = Lion
Red Uses : Physical resilience. Power. Sudden change in circumstances to wielder's benefit.
White Curse : Inherent danger. "Danger finds you."
DARK GREEN SPHERE : Beam Guardian = Turtle
Red Uses : Monetary Prosperity. Healing. Manifesting & creation. Increased luck when dealing chance.
White Curse : Bad luck.
INDIGO SPHERE : Beam Guardian = Hare
Red Uses : Emotional manipulation of others. Defense against mind control.
White Curse : Emotional instability.
PEARL GREY SPHERE : Beam Guardian = Rat
Red Uses : Seeing into Todash Space & the Prim. Reveals secret doors & dimensional portals. Invisibility.
White Curse : Thinnies.
LIME GREEN SPHERE : Beam Guardian = Elephant
Red Uses : Seeing past-lives/past ka-cycles. Astral projection.
White Curse : Disassociative personality.
AZURE SPHERE : Beam Guardian = Dog
Red Uses : Truth finding. Forcing confessions from others.
White Curse : Condemnation.
BROWN SPHERE : Beam Guardian = Bear
Red Uses : Animalism. (Control over animals to varying degrees.) Magical grounding. Deepens one's meditative state when doing inner workings.
White Curse : Animal agression towards the wielder.