Superphil
Dismember
Its because green is a colour that is particularly troublesome for people who are colour blind. I'm not sure if the exact details, but the ban is in consideration of colour-blindness.
Edit: Just found this: https://www.bbc.co.uk/sport/football/57880378
Speaking as someone who is colour-blind, and specifically red/green colour-blind (the most common one) the problems I have are not with green shirts, but when the refs wear yellow, the away team wears orange and the goalie wears a light green shirt. Or if between the teams and referees wear any combination of light yellow, gold, orange, light green, beige or mustard (Barber), that's when the confusion sets in for me. Green goalies shirts, or green outfield shirts are generally fine, so long as the opposition isn't wearing red.
Then again as it's the FA, EPL, UEFA, FIFA 'dealing' with it they probably haven't done any research with colour-blind people, they've probably just decided that they know what is best for us so we have to accept it, screw your traditional team colours Plymouth, Ireland, Sassuolo and Venezia, UEFA is going to do what it wants to do regardless of anything you may feel.