So you point the heat gun directly at the plastic where the white marks are and, hold it there till the marks go away? That's it? how do you know when it is as good as it gets? Or, when is to long befroe you blow a hole in the plastic?

that is so weird that it can turn it back to the original color or, close.

 

I have done this and seen other get good results too and you can also use a small butane torch.

You will need to pay very close attention to not be melting the plastic cause then your buying new ones, and this is real easy to do especially with the torche.