As I understand it, not all species commonly referred to as 'newts' are dependant on their diet for their coloration. I can't remember where the split occurred, but I'm pretty sure that the Tylototriton/Pleurodelese family were among the species that produce their own orange/red pigments without having to ingest it. I'm still searching for the paper I read regarding this, I'll post a link when I do.
Mind you, it would make an interesting experiment to raise two groups of T. shanjing on separate diets with high and low carotenoid content to see if it will enhance the natural colour they already have.