New York City's green cabs are not any different or any more environmentally friendly than regular cabs. Customers cannot hail green cabs inside of Manhattan.
Green cabs can drop passengers off in Manhattan, but rides cannot originate from there. Green cabs are the result of a 2013 initiative by the mayor's office to increase the number of cabs in the area to meet rising demand. There are no environmental considerations to this program, and the color green was selected for the cabs simply as a contrast to the traditional yellow cab. It does not indicate a reduced level of environmental impact.