When you live at home, you live under your parents' rules. When you move out, then you make your own rules. When you go back home for a visit and there is some argument about your hair, etc., you can simply smile and say - "I like it this way."
Be respectful when speaking to your parents. Hollering - "You can't tell me what to do - I'm 19 years old!!" tells everyone that you're still a child. Adults sit down and talk through issues.
Generally speaking, your parents want the best for you, so think of that if you decide you want to smart off. It's not worth World War 3 just because you want a different haircut, or different jeans or whatever the problem is.
Get a job, save your money so you can move out and be independent. Until then, if you live with them, you have to abide by their rules.