User blog comment:Fliu/Chapter 949: Victory at Udon/@comment-184.163.186.15-20190720023244/@comment-108.83.222.210-20190720041359

He has demonstrated great proficiency with it, but we cannot say for certain what mastered means in terms of haki since ideally one should always improve ones skills with it due to the likelihood of meeting someone better with either the basic or advanced forms. He seems to be able to use it at will if that is what you are saying. Luffy has shown great skill with all three colors of haki, but I look forward to seeing how far he will continue to go with it. I would hope that he would continue to work on improving all three forms as times goes on. Of course, that would go for improving his other abilities as well. It is always a joy to see characters continue to improve themselves.