Answer:
The easiest way to do this is to get a bottle of ketchup, comb it through your hair leave it on for a couple of minutes, rinse it off in the shower, shampoo twice and then condition it, it sounds strange but its a great trick and pretty cheap instead of having to go out and buy some professional product that costs silly amounts, the acid in the ketchup actually lifts the green/grey tint from your hair and it definitely works, hope this helped :)