Why do all chinese people have black hair?
They do not all have black hair. If you look closely at the hair of Asian people, it varies in shade from very deep black to medium brown with reddish highlights. The reason their hair is almost always quite dark is that there are not a lot of interracial marriages in China. For the most part, Chinese people in China marry other Chinese people, so the children have the same Chinese lineage on both sides, hence the dark hair. If Chinese people started marrying Caucasians more frequently you would see many more variations in hair color, eye color and features.