If I RE dye my hair from fake blonde to Medium brown like Cheryl Coles colour with a box dye at home will my hair go orange or green?

That depends. If the fake blonde is like a BLEACH blonde or Really light , It might turn green, But if its bleached it will turn green, So if you have bleached it Leave it in for about an hour. That's what I did. The ending result turned out great ! I hope this works for yhu.