White Raven's History
White Raven is a special form that Raven has assumed under unique circumstances, four times throughout the series for multiple reasons. White Raven is Raven's most primal, significant and powerful version of herself, mostly shown as a symbol of her highest hidden power and her inner purity against the consuming evil of her father.
The first instance occured in Nevermore within the multidimensional realm of Raven's own mind: an ethereal place where Raven's separate emotional forms are capable of independently existing. Raven, whose emotions had become unbalanced and her Rage unleashed from within during the Titans' earlier battle with Doctor Light, discovered that Beast Boy and Cyborg had come upon her mystical mirror (a meditation tool enabling anyone who holds it to be drawn into her mind) and had used it access her own subconscious. After encountering three different emotional forms of Raven (with each symbolically wearing a different color), Raven herself enters and confronts them, but her Rage Form (known as Trigon) quickly manifests and attacks them all. Though Raven insists the two leave, Beast Boy and Cyborg instead choose to stay to hold off Trigon while Raven, on a suggestion from Beast Boy who said they were all part of who she was, summons all her emotional forms and merges them with herself to create a "white" form. She then projects a stream of energy from her hands at Trigon, overwhelming him and merging him back into her soul. Raven then returns to her original blue self once again and the group exits her mind having not only gained victory, but two true friendships.
The second instance occurred in an alternate future, one which Starfire prevented from becoming the true future of the Titans by returning to her own time era, in How Long is Forever?, after the high-tech, time-traveling genius Warp goes back a century to Jump City to steal a clock, to be met with the Teen Titans. Starfire manages to leap into Warp's time portal and damage his vortex regulator, thus stranding them both at two decades in the future instead of ten. She encounters a far older and more damaged Cyborg, who gives her the current whereabouts of Beast Boy and Raven. Raven is alone in a pure-white room, her sanity having been lost and her mind broken from her loss of friendship, in a white form with a black leotard (with a white hue because she can't still control her emotions), shielding Starfire away from her because she thought she was yet another "figment". Though Starfire eventually manages to find Nightwing (Robin), who gathers the Titans once again to defeat Warp and regress him back to an infant, with Raven's telekinetic abilities contributing to their prevailing, Raven is still seen in her white form as Starfire returns with the clock back to her own time and recounts her experiences to the Titans, Raven included.
The third instance takes place during the events of Spellbound, when Raven, feeling isolated from the other Titans because of her "creepy" nature and different interests, takes solace in Malchior, apparently a benevolent yet powerful wizard who vanquished the dread dragon a thousand years ago with the same enchanted book that fell into Raven's possession. With her own mystical powers unable to break the curse that had apparently trapped Malchior within the book by Rorek's last curse, Raven is offered to simply "talk" with him, and, being guided by Malchior, prepares a potent spell to release his soul from the book in the form of its pages in the shape of a human body, though he is still bound. Attached to Malchior and seeking to help free him fully, Raven asks to be taught far more powerful magics from millennia of magical knowledge and over six thousand pages of such spells; Malchior eventually magically transfers all the lore into her chakra and mind, enabling her to master the mystic arts and project a green version of her raven soul-self. This emotional upheaval through her intense love for Malchior, love which she had not yet felt as deeply for anyone else, possibly combined with the vast augmentation of her powers and arcane lore, changes her back to the "white" Raven yet again. Raven now possesses vast powers at her command, but is unable to exert great control over them, as shown during a rematch with Kardiak; Raven discovers that this is "dark magic", but Malchior tells her that it is simply "power", called only by those who fear it "dark" and convinces her to free him using the spell he had taught her. However, Malchior reveals himself as actually the dragon, not the wizard, having changed the names secretly, and battles Raven after defeating the other four Titans, with only darkness in his heart and malice for her. Raven uses Rorek's spell to again imprison him within the book, reverting back to blue after she does so.
The fourth and last known transformation into her "white" form occurs during the considerably darker fourth series, when it is revealed that she is daughter to Trigon, malevolent demon lord who seeks to destroy Earth and the entire universe it. As shown in Birthmark and The Prophecy, Raven, born in Azarath, was foretold to be doomed to a terrible fate: the "gem" and "portal" of Trigon directly into the Earth dimension. With their old adversary Slade resurrected and empowered with terrible demonic magic granting him sufficient might to rival the combined forces of the Teen Titans, and Raven fearful of her own fate and that of all existence's, Raven reveals her tragic past and future to the Titans, who strove to prepare against the oncoming tide of evil that would besiege the world and their old friend, unknown to a secretly hope-dead Raven. As the sun is eclipsed in shadows, Raven collapses, unable to hold back horrified tears at what is happening, and the planets align to ready the position of the Portal to Earth, the Titans place Raven in a state-of-the-art security room reinforced with the united efforts of all their resources and shielded by an additional layer of protection with Raven's own mystic runes from her books.
But Trigon's bond with Raven proves far too potent and deep to be blocked by any means within their grasp, taunting her and insisting it was her destiny to bring him forth into the world, that she could not hide her fate and her friends were still fighting for her at their expense. The Titans attempt to attack Slade and his forces, but are quickly defeated, despite all their desperate efforts and determination, to be saved from complete destruction by Raven's intervention, when she agrees to go with Slade to grant Trigon access to Earth's dimension, giving the four Titans a farewell blessing in the form of a portion of her own powers as a final defense. Shortly afterwards, the Titans try to dissuade Raven from sacrificing her life to act as a gateway for her father, whose very presence conquers all of Earth and disables everyone except the remaining Titans.
They are led to Slade, who had been betrayed by Trigon and stripped of his powers. Slade then tells them that there is still hope of saving the world with Raven's help. After Slade and Robin fighting their way through a "Hell" of Trigon's demonic minions, depending on the other three Titans to divert Trigon's attention, the two part ways, knowing that this would be the last time they were ever to join forces as one, with Slade reclaiming his life and flesh fully and Robin, following the raven, finding a younger version of Raven, garbed in white, under a graphite cloak.
Though Raven initially appears to not know or trust her former friend and attempts to flee from him, claiming she was "lost", Robin convinces her to place her faith in both him and herself. Raven has retained at least some part of her memory, but tells Robin the situation is still hopeless, with her powers having originated primarily from Trigon's.
After a perilous journey to the ravaged realm above, Robin and Raven meet with the other three Titans and all the Titans except for the regressed Raven engage in a last clash with Trigon, Slade coming to their aid at a crucial moment, their joined forces even managing to hold their own against him and physically injure him, but the demon's power is too great and they are all completely overwhelmed, with only Raven remaining.
An attempted death-blow to permanently finish his child is inexplicably foiled by her own power. Trigon cruelly tells Raven that she lives only because of his allowing it and she is powerless still against him, despite whatever small fraction of power she still bore. Raven then taps into more of her power and actually returns to her previous form, albeit still clothed in white, and tells Trigon coldly that he may have created her, but he was never her "father".
Raven attacks Trigon, knocking him back, and, with a final declaration of Trigon not being welcome to her home and that of her friends, unleashes her white soul-self to envelop and obliterate Trigon, cleansing the dark stains he had left upon Earth forevermore and reverting back to her original blue form. She says to Robin, perhaps fittingly, that "In the end, there really is no end - just new beginnings". With that, she marks the start of a future she would carve out by herself freely, shaped only with her friends and having conquered the destiny she believed she would be eternally bound by.