Do you know of any natural recipes for fading semi-permanent hair dye?

Very long story-- I'm sorry, but I really need some advice.

I tone my heavily-highlighted hair with Natural Instincts 06 Linen. I've used it 3 times before, but when I used it this weekend the lightest parts of my hair ended up with a really awful drab ash tone. It looks blue-grey in some lights. Other times it's more of a grey-green. I usually get a slight mauve cast to my lightest highlights when I tone, but it always washes away after the first shampoo and then my hair looks great. This colour isn't budging, though. I don't know why this happened. I know overly-porous hair can grab up too much dye, but my hair looks and feels really healthy.

I've tried washing my hair with dish liquid and dandruff shampoo a number of times. I've also done a couple of deep conditioning treatments and two virgin olive oil wraps, but the ashy grey tinge is still there. The part that isn't ashy is a really pretty neutral blonde with a slight hint of gold. I don't know what to do about this. I certainly don't want to use anything harsh on my hair.

Does anyone know of anything that will help to fade this colour?

Any suggestions and advice would be greatly appreciated.

P.S. The ashy colour is mostly on the top 6" of my hair; the other 18" looks good, so a hair cut is out of the question.

Thanks Rosebud. I actually gave in and did some colour correction on my hair. I used L'Image Ultra Light Natural Blonde for 10 minutes to get the ashy tone out of my highlights. I then put some colour back into the highlights and toned down my roots with Nice 'N Easy Medium Champagne Blonde. It turned out really well (and my hair still looks and feels healthy). I'm going to leave my colour alone for a while now. :-)