This is no question in quality, Jotaro's hat and hair need no defining line as to where one ends. They just are.

That was a thing in original manga – both Jojo's hair and hat are black and blend together when drawn, so the author occasionaly screwd up by drawing hair on the back of a hat. When called out on itt he made a pokerface and continued to draw Jojo like that on purpose.

Since then Jojo Cap-hair is a thing in Jojo fandom.