I went to my hairdressers recently to have a colour put on she put a dark brown on and this went green then she put a black on and its turned blue what can I do to get it back to black

Dying light colored, or blonde hair brunette can cause it to turn a greenish color. There's a good chance that the black hair dye reacted with the brown hair dye. Hair dye can react to your shampoo, medicine you are taking, even minerals from the water you use to wash your hair. I suggest looking into a professional hair-colorist who may have products to reverse the discoloration. Otherwise, I would let it grow out in the mean time.