How to get rid of red tones in my hair

I previously had highlighted hair and wanted to go back to my natural medium brown color. I was told i had to pick a reddish color so my hair didn't turn green, i picked up a medium copper color. It was very dark at first and now its faded and all you see is red. Can i use an ash tone? or Mix a light brown and medium ash brown together i have on hand to prevent turning my hair green..help :(