What the hell are you talking about, evidence? When was the last time you saw a naturally blonde Korean? Or one with blue eyes, or curly hair?
It's a matter of having bred within a certain (very large - I'm not implying anything bad here) gene pool, until the dominant genes are so dominant that the recessive ones almost never show themselves.
Over the years I have tried to train myself to differentiate between various Asians and can now--in a reasonably reproducible manner--differentiate between Vietnamese, Koreans, Chinese and Japanese. While the differences among them may not be as clear as those between red and brown hair, they do exist.