what was the original color, what is the current color & what is the carpet made of? nylon, olefin, wool, etc...?
without seeing it my response is:
no it can't be reversed. it is most likely color loss. his options are to have it dyed, live with it or replace it. it can't be "cleaned away."
but that could change if it were olefin(plastic), which bleach will not affect since the color is solution dye (mixed in with the liquid plastic before the carpet is made.) i may have gotten some verbage wrong, but that's the gist of it.
plus who knows what the prospect really used on it, you can't know for sure. many ppl do not tell us exactly what they did to a carpet, or how they did it.