Skin color is indeed related to UV radiation. In the equator, there is higher UV radiation due to the tropical climate in the equator. The equator is at 0 to 20 latitude therefore at this location, darker skin are found because darker skin helps protect from sun damage. From the temperate regions at 60 to 80 latitude, lighter skin is found as UV rays are not as potent compared to the equator.
The correct answer is dark skin at 0-20 and light skin at 60-80.