Is a change in venting system required for Green Hydrogen projects? If yes, how do green hydrogen projects differ from blue or brown hydrogen projects?

The colors of hydrogen are not different hydrogen molecules. The colors represent the different methods to produce hydrogen. The colors are based on how much carbon is produced into the atmosphere during the manufacture of hydrogen. 

That being said there is no difference in hydrogen vent systems design by color, only by the design parameters (i.e. temperature, pressure, flow rate, etc.)