If it's just discolouration G3 cutting paste followed with a good polish then wax along with plenty of elbow grease.
Apply G3 sparingly and use a random orbital polishing machine. Keep the surface wet and do not allow the gelcoat to get warm/friction burns. When the gel looks ok apply polish and the orbital polishing machine then finish off with hand applied and buffed up wax.
Thats what I used to do with Awol's blue hull. I now have a tendency to pay others to save my sore arms
Apparently, she does a very good job