It's a fact Lucas had ownership of TESB and ROTJ before the films were even made. It's a fact he hired everybody who ever worked on those films and paid them with his own money to do the job he wanted done. Lucas' description of history is accurate enough, and his belief in his right to alter the films is understandable enough. They were literally made for him.

Turner bought rights to existing films that he had no prior business or artistic connection to, and started tinkering. There's no moral equivalence between Turner's colorization of films and Lucas' continuing creative control of Star Wars.

Lucas' comments against colorization are about the original artists' right to control their creations. Lucas considers himself the lead artist who hires other artists to contribute material that he then selects or rejects to fit what he wants. He collaborated with people 20-30 years ago to get it the way he wanted then, and now he's collaborating with other people to get it the way he wants now.