This is going to sound crazy, but wash it with Tide powder detergent (original). This will fade it over time. Once you have faded it a couple shades, then use Dawn dishwashing detergent (for handwashing your dishes--the plain yellow kind)
I had an accident where my hair turned blue-black---YUCK! My stylist gave me this advice. It worked, but it took some time and my hair wasn't really healthy until it grew out, but at least it helped fade it. It also will depend on what kind of dye you used. I used Nice n' Easy so that was a problem. He also said that Feria is very damaging if you try to change it. Good luck!
at 2:36 AM on Sep. 11, 2009