Yes, definite correlation of skin tone in the development of the different human cultures and groups and how close they were to the equator and amount of sun. Darker skin is a result of more pigmentation, which helps to protect the skin from the sun. As to some cities being cooler despite being close to the equator-- two big issues there are usually why: coastal winds if they are near or at the coast of the island or continent, and elevation. Constant cooling breezes on the coasts keep many cities comfortable even though inland the temps may be very high and with high humidity. Elevation has a big impact on temps, a great example is Nairobi, Kenya, located at 1°17′S 36°49′E, essentially within miles of the equator. It has perfect weather, per my brother who lived there a while. Day temps rarely get above 75 degrees F, coldest all year might be down to 48 F. Its altitude has a lot to do with that-- at about 5,450 ft in elevation. A mile above sea level, and in a wide plain where cooling breezes can keep it cool.