Question

why our hair color is black not pink,red,blue nd purple

Answer 1

Because the skin of our hairs produces "melanin" that keeps our hair colour black
Hope this helps you......☺

Answer 2

Black is the most common hair color in the world, and is due to a large amount of eumelanin.  Brown is also common, and is due to eumelanin mixed with a bit of pheomelanin.  Blond is only found in about 2% of the world's population.  It is due to very small amounts of melanin.  Slight amounts of black, brown, and red make for all the variations we see in blonds - such as ash, flaxen, and strawberry blond.  And red hair is the rarest of all, about 1% of the world.  It is due to high levels of pheomelanin plus low levels of eumelanin.

If you are curious, gray hair is due to nothing but a little black melanin, and white hair is a matter of no melanin at all.