A green tint to your coloured hair is usually caused by using ashy colours, such as ash blonds or ash browns. Ash colours can be pretty and natural looking, but some hair doesn't take to ash colours well. In these cases, the ash covers the desired colour with a green or grey tint. Since you now know that your hair doesn't take to ash colours, you should stick to warm colours in the future. In the meantime, there are a few steps you can take to relieve your hair of the green tint.
Wash your hair with a clarifying shampoo. You can purchase clarifying shampoos in most drugstores. These shampoos contain ingredients that equalise colour balance throughout your hair. There are specific shampoos for red tones and for green tones. Wash your hair daily with a clarifying shampoo that removes green tones. You should see results after the first wash. If your green tint is minor, you may only need to persist with clarifying shampoo for a few days.
Apply a warmer toned dye. Green tints most commonly occur from using an ash coloured dye. In this case, your hair will accept warmer tones better. Warm tones consist of auburns and light browns. These tones will counteract the green tint in your hair. Consider choosing a warmer tone to dye over your green tint. The dye will take nicely and rid you of your green tint.
Re-apply same coloured dye. If you are adamant about achieving the colour you originally chose you can attempt to re-apply the same colour dye. Sometimes, the dye penetrates the hair follicles a second time and removes the green tint entirely. There is also a chance you will worsen your green tint.
Apply temporary coloured hair wash throughout your hair. If you would like to take no more chances nor damage your hair any further, choose a temporary solution that will mask your green tint until it fades. Temporary coloured hair washes are like leave-in conditioners. Apply a moderate amount throughout your hair while it's still wet, after you wash your hair.