Board Thread:Off-Topic Discussion/@comment-4870649-20130925153847/@comment-3467648-20130926225438

You could use it for dramatic effect. e.g.: When she is angered her hair turns red, when she is depressed it turns blue

I mentioned this because accord her official twitter mentions her trait of vary her hair color. If you think it's a bit weird, you use a partial color change, like a gradient color change that  affects mainly the hair tips.