The human has the hair colour in black from their birth. Once we are aged, hair becomes grey or white in colour. Some people will have the black colour even they are aged. These all changes are based on life style, ageing, genes and food. Now we can see how hair is black? If some thing has to grow, there should be some source. For example, trees or plants are growing by source of water. The same, hair is growing by the source of blood. Blood contains hemoglobin and oxygen. This hemoglobin contains iron. When this iron will react with oxygen, the colour change will be black. For example, When you are injured, the blood will be released from your skin. It immediately reacts with oxygen comes from the outer air. The blood colour will be changed black. The hair substance also get this black colour because of this reaction. When our blood has the enough iron content (hemoglobin) and flow to the b...