Everyone has the right to do whatever they want to become popular, as long what they do doesn't hurt others. Some may look down on people who do everything they can to gain popularity, but they have no right to try and stop them. If the person hurts themselves while trying to become popular, that is on them.
If changing their hair color makes them more popular, then while that is a bit shallow and selfish, it is the fault of their fans and not them. Hair color has nothing to do with talent, so the only thing affected is how the fans view them, and if the fans are swayed by something as little as hair color, that's on them. Celebrities should do it and they should not; they should just do what they want. There's no reason that they have to either do it or avoid it.
It is my belief that celebrities should use their access to large numbers of people to do some good. If a celebrity changes their appearance because they feel it makes them more desirable, someone at home who shares that original characteristic or trait is made to believe that they are somehow ugly. As a society, we can't send the message that there's only one way to be attractive or liked. We should embrace all appearances, and it's important for celebrities to be a part of that conversation.
The celebrities should not change their appearance to become more popular.I believe their work or talent should make them known instead of their appearance. Copying the appearance of people more popular is not a way to gain popularity as that is kind of faking. If they work hard and have the capability they can become popular on their own keeping their own self. They should make themselves in a way that people would like to copy them and not the other way around.