I would just spend ages petting him all over, gradually working up his neck, and retreating when he shows fear, so he understands you don't want to hurt him.
I'm afraid that you have the 'approach and retreat' training method all backwards.
You keep pursuing the horse and the untouchable area and only retreat when he relaxes and accepts you going to a certain area.
If you retreat when he objects, you are training him to throw a fit and object so that he can train you to back off.
I suggest you get a 5 foot stock whip and use it to 'pet' him with. Treat it like it is an extension of your arm and hand. Snap a lead on his safe-halter and use that to keep him from turning his butt to you and then get him accustomed to being petted and rubbed on his face, neck and poll.
Keep petting an area until he relaxes and then reward him with backing away and letting him think about it. Then go back and pet some more -- each time getting closer to his face, poll and muzzle - all touch-me-not areas on a green colt. Just never back away until he is accepting more than he did last time.