Hmm. Synthetic hair fibres (esp Kanekalon) are extremely color fast. A lot of times, the pigments in plastic are chemically bound to the polymer/monomer. Since synthetically derived pigments are composed chemically different than melanin, it is not going to be the same process.
The only thing I know that can partially destroy the pigment is industrial strength Hydrogen Peroxide, and they don't even sell it that concentrated to the general public or hairstylists.
Sorry I couldn't be of more help to you.