I'd like to see the HOA make an attempt to place a lien on his house for this (which is really their only "legal" resource to enforce their regulations).
You clearly haven't dealt with HOA's much. They do this kind of stuff all the time, often for piddly stuff much less visible than this. The HOA where I used to live fined someone for painting the pole on which their mailbox was mounted a shade of black that wasn't allowed. He played the tough guy and refused to repaint the pole. They fined him, and slapped a lien on his house when he wouldn't pay. In the end he had to repaint and pay the fines.
HOA's can be very powerful because as a resident you have willfully agreed to abide by the regs. You don't have a legal leg to stand on if you refuse to go along with the regs, unless the regs themselves are illegal, which is unlikely. The people running the HOA also are usually also not paid anything, so it's not like they are afraid to do something unpopular and get voted out at the next election.
You'd be surprised at how far some HOA's will go, and they have the legal right to do it because you agreed to it when you moved in. It's like dealing with the IRS. Sure, you have rights, but at the end of the day, they can make your life miserable and you don't have a whole lot of recourse.