well you wouldnt need to bleach the top bit to just tint it darker, thats probably why its gone green to much ash on hair way to light. use a semi black or 3/0 so its not so harsh, and i say semi so if when the client wants something different, your not going to have a big palava getting that black out. then for the gray colour, i would used 12/1 say for instance 30mls 12/1 with 5mls of 2/0 .. then your peroxide maybe 5 vol or 10 vol depending on condition of hair. i have gray hair myself and this is what i done on myself, and two clients. at first i thought REALLY! with the mixing ratio but its incredible really. just dont overdo it on the black colour thinking it wont be enough because it will come out like iron gray!
hope this helps..