I have always thought darker colors absorb more heat from the sun, so if you are wearing a white T-shirt you will be cooler under sun than wearing a darker T-shirt, or a black piece of steel will be hotter under the sun than a shiny silvery one.
If this is true, then why is the same not applicable to skin color? It seems to me like the more sun in an area the darker the people's skin has become, isn't that the case?
It isn't about heat but ultraviolet light. Melanin is the pigment that makes our skin colour whatever it is and in darker skin there's more melanin. Melanin dissipates UV, which otherwise would cause skin cancer as it introduces mutations into DNA. Melanin production is stimulated by UV so that's why tanning beds work, our body senses the danger and responds by making our skin darker. Yes this makes us hotter but that's a small price to pay, melanin needs to be dark to do its job well.
I agree with what has been said here about melanin and UV light, but I think there is a missing piece to fully understand the color variation in humans. Otherwise everyone would have just black skin and problem solved.
One of the counterparts appears to be the conversion of Vitamin D to an active form, that requires the action of sunlight. This trade-off explains the beautiful gradient of color in human populations *.
I think that you'll need a biologist to answer your question fully. However, I can try to explain what I can in terms of physics. Generally, the darker a material is, the greater the range of wavelengths of light it absorbs. With what is perceived as a perfectly black material by a human reflecting no wavelengths of the visible light spectrum of electromagnetic radiation at all. Therefore it would be logical that in cold climates humans would have darker skin colors in order to absorb a greater range of wavelengths of light. Although at first glance this seems the correct way for humans, and in fact all organisms to evolve, it's obviously not the case. There must be other underlying reasons that have caused organisms to evolve the way they do. An interesting example of how nature seems to defy this is leaves. One would think that the chloroplasts that make up leaves should be black in order to absorb sunlight as efficiently as possible. As we know, this isn't the case.
Yes, it is true that the hotter the sun, the darker people's skin becomes (in general) because of the evolutionary advantage conferred by having melanin to protect against UV light. The reason a dark object like an asphalt road gets hot quickly is that colors like black absorb most wavelengths of light, and therefore absorb more energy in the form of thermal energy.
In the same way, the melanin in your skin absorbs the UV from the sunlight because it is so dark, and protects your skin from it.
to answer your question from years ago maybe to better inform any new readers that read this. yes and no. we have melanin in more areas than just our skin, it's in our nervous system, in our eyes, and etc and we should also ask what "information" we obsorb in those areas. having melanin does make it easier to absorb all wavelengths on the electromagnetic spectrum, but not everyone with dark and lighter skin can live easily under the sun. also consider what i call "inorganic" or "chemical" EMF/wavelengths highly melanated beings are receiving from computers and other man made devices which there are links to cancer and other issues in the body from those unnatural EMF. Research has shown that most bodies whether light or darker can't survive past 104F because the thermoregulatory system shuts down. now if it 120f outside does this mean that your body is the same temp,,, i don't feel so after being exposed to such weather. i have light skin, but can develop melanin rapidly with minimal damage or sunburn occurrences. but my auntie who is darker than me, who has lupus, cannot be in the sun. this is on an individual basis, but having more melanin or active melanin in general to protect you may be more in your favor, especially this 2017 and upcoming years. the color white is said to block the UV rays, but not absorb most of it. this poses the question to cancer caused by over exposure to the sun and the hue you are as man, if you are of darker hue and do not have any sun exposure, you will or may have more health problems, little to no active melanin or light skin, you may or may not have more health problems in the sun or certain longitudes and latitudes. this is good to consider whether you are aligned in a place where you are getting the correct amount of sun exposure, or consider if you are getting the incorrect amount of sun exposure. again, this answer can only be answered on an individual basis.