If it is plastic i do not understand what is mean by taking the effect off? I would clean it as per a regular plastic seat.
If it is painted wood or MDF then i would be more hesitant. When it comes to loo seats I have in my experience only ever cleaned with a soapy or disinfectant cloth. Whatever stains were left were left, that is the clients problem. The green may well be a reaction from any metal parts on the seat when it comes into contact with bodily fluids, water, or toilet cleaning products.