Why do people have different skin colour

People have different skin colour mainly due to genetics and the radiation from the suns UV rays.
Generally people who live closer to the equator have darker skin than those who live nearer the poles. Skin absorbs the UV rays from the sun and can turn a certain amount of this into vitamin D. In countries near the equator people absorb way more UV rays than is the amount for vitamin D. The UV rays then start to tan the skin. Over hundreds of years peoples skin has got darker and darker.
In countries nearer the pole we don't get enough vitamin D so therefore don't have as dark skin as those who live near the equator.