White is one of her least favorite colors. It represents all that is pure and whole. Both of which she never was, never will be, ever. Her soul is tainted; its color is the deepest shade of the darkest night.
Her mind is jumbled. Time has no place here in Nevermore. It is lost, forgotten. A curse, a blessing, only one of which she is privy to. Although there is no concept of time in her deeply guarded cell she can still remember the day she left the Titans. The day she ran, the day she hurt them.
Not that it matters.
She supposed she would have fallen apart anyway. She wears white because she has locked herself in her own personal insane asylum. It's twisted that he wears black now. Or so she sees in the nights when her barriers slip ever so slightly. A haunted man, in black with a blue bird on his chest, flying through the night. Not that she wants to know. This is exactly what she has been avoiding.
Leave before you are left. And so that is what she did.
Everyone could see the way they looked at each other, the little glances when the other was not looking, the brief touches. She didn't need her visions to tell her that they would end up together. They only confirmed it. So she left, packed up her things for the sake of her friends. They would have never understood. She knew that her feelings for him were growing and it was better to let them never appear. She left the next day.
Their sad faces appear in her nightmares when she actually sleeps.
White was the color when she was purged of her father. When she used all her emotions. Now it is the color of emptiness. This is why she really despises the color. At least in the darkness she was never alone.
She covers everything in white to remind her of all she is. Empty, emotionless, eradicated. This is the way it was meant to be.