Last year I tried and the last color after fading was light green. And how long hair dye maintain in your hair depends on two aspects:
1.Type of dye

>Permanent dyes: Minimum a week. Longer is better. I would wait until you can't bear with the roots before you touch up, but after 5cm it can get tough because the hair close to the scalp develops really fast.

>Bleach: Minimum two weeks. Longer is much better.

2. Conditions of your hair

> If your hair is damaged and dry the hair dye is not go long lasting.