Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. It only takes a minute to sign up. All people don't have those hair colors. There is no deep reason for those traits other than "that mutation happened to occur and spread through this population".
Breaking The Asian Myth About Asian Hair - Character Media
Due to these differences, hair does not grow in the same way or at the same speed in people of different ethnic origins. Asian hair is usually straight and either dark brown or black in color. It grows perpendicularly to the scalp. This hair type has the fastest growth rate at approximately 1. A strand of Asian hair has a somewhat round, even shape. Nonetheless, Asian hair has the lowest density of the three ethnicities.
Do some of us have sleek, black, and straight hair? Of course. Do all of us have this? Absolutely not.
Black hair is the darkest and most common of all human hair colors globally, due to larger populations with this dominant trait. It is a dominant genetic trait, and it is found in people of all backgrounds and ethnicities. It has large amounts of eumelanin and is more dense than other hair colors. In English, various types of black hair are sometimes described as soft-black , raven black , or jet-black. The range of skin colors associated with black hair is vast, ranging from the palest of light skin tones to dark skin.