You'll have to Re-dye the area, heres a link on home made black dye we humans have been making since god knows when, carefull, wear latex or rubber gloves because it's powerful.
http://www.primitiveways.com/black_dye.html
Use a sponge an apply to the area or dunk the whole thing in the vat if you can, it'll all even out unless it's a multicolor shirt........then you'll have to sponge just the areas needed.......if the bleach took out multiple colors on the same shirt (like my underwear), then you'll have to either dye it ALL black........or make some more dye of the same color........depends if it's worth the time N effort, I say just go one solid color, damage done is done........unless it's a $100+ piece of clothing, not worth the hardship.
Darren
May 2007