I have heard about mixing laundry detergent with your regular shampoo to make it fade faster. Please be careful about stripping and highlighing hair. I've had my hair turn to gum because I tried to strip a black out of it (it was done at a salon). It was HORRIBLE! I just recently had to cut it short because the split ends where it had broken off just kept riding up the shaft and where in various lengths all over my head (the whole stripping accident happened over three years ago!). It sucked!
I was told to never use home dye kits EVER again. Well I DID use one last year. It was supposed to be dark brown but came out as BLUE BLACK! Now, this color looks good on me so it wasn't too bad but I wasn't expecting it. However, if it makes you feel any better, after a week it had faded to dark brown. Then it faded some more and you could tell where my highlights were.
Recently I had my stylist put in dark chocolate lowlights, over my highlights. Well those have faded and you can tell where the highlights were. I need to go back and get them lowlighted again.