Green/black hair

Providing you don't want to go to a salon to get it fixed for good....There is a red shampoo you can buy at the beauty supply shops called Complements. You want to use red to counter the green, doing this should turn the green parts a shade of brown. I would buy the more orange shade of red for maximum green countering, and if you don't want redder hair than you have now, wash your hair with your normal shampoo and conditioner, let it dry, then afterwards wash only the green chunks of hair with the red shampoo. You will need 2 or 3 washes with it to notice a difference, try to let it sit on your hair for 10 minutes before rinsing it out, and don't condition those pieces afterwards (to keep the maximum amount of pigment on your hair). It doesn't dye your hair, just deposits pigment on it, so after you wash once or twice with normal shampoo, the red will disappear. To keep even more red on the green pieces, just wash them with only the red shampoo and never the normal shampoo.

Sounds like a pain huh? I used to have to do it when I had green hair. You will probably get sick of the time it takes and want to go to a salon to get it fixed permanently.
Good luck,