I've heard that head and shoulders works - but I have never tried it. I suppose you could always go back to the hairdresser's and get some streaks put in to lighten it?
most dyes actually fade themselves over a few washes, in my experience anyway. just be wary of the colour it will turn when it does. if you are really desperate though, washing up liquid strips hair dye more than shampoo, it sounds crazy but trust me!
Head and Shoulders does not lighten your hair. I use that on a regular basis, and i have black hair and it's still black. Just thought I'd let you know. :)