I got similar lightening results as ChilmarkGryphon:
I dyed a white heat-resistant fiber wig with FW Ink Method, and attempted to remove all color.
First, I soaked the wig in a plastic baggie filled with rubbing alcohol overnight and rinsed with water. This bleached out the color about half way.
Next, I sprayed the wig with OxyClean MaxForce spray laundry stain remover. (From WalMart)
I sprayed the wet wig thoroughly, lathered it, and put it in a baggie again for a few hours, rinsed, and repeated.
I'll try to find some pics. It was originally a white wig, dyed bright orange/pink (don't remember), and I got it to a very, very faint pink. But it definitely still has a tint to it. The wig fiber is matte and waxy feeling, like when you use too much fabric softener in your clothes, because the Oxy Clean probably has some softener in it. I suspect that washing with a dish soap might remove the waxiness. But it does smell really, really awesome.
LEFT: White Cosworx Premium wig dyed with FW Ink method - red and white dye mix to get a nice bright pink.
MIDDLE: Wig after rubbing alcohol applied overnight.
RIGHT: Wig after OxyClean soak. I did the OxyClean a second time and got it a bit lighter, but have no pics.
Definitely not the best method. The ink seems to leave a permanent stain. Which is a good and bad thing, I suppose, depending on your intentions. I hope more people experiment and post some more success stories!
EDIT: Ani_BEE, I'm surprised you didn't get consistent color! I used a spray bottle and have dyed 3 or 4 of them for tutorial's sake, using both 70% and 90% Alcohol (70% is best I found - more shiny) and have gotten the results above - no streaking at all. What method are you using to put the dye on the wig?