Ketchup....
Now don't look at me like that, I'm actually not joking!
I watched a thing with that bird of GMTV once... Lorraine Kelly?.... and I swear she said that if you ae getting greenish tones to your hair try using ketchup. I asked my hair dresser about this and he said it was true.
Now before you take this advice, it is worth knowing that I can occasionally be accused of being gullible and my hair dresser used to be a builder.... (I'm not kidding about the latter but he is very good).
But still... try it. I'm honestly, honestly not joking.