In general, people with darker skin tones (i.e. with more melanin) are less likely to suffer from skin cancers triggered by exposure to high energy photons in sunlight.

It has been traditionally believed that skin pigmentation is the most important photoprotective factor, since melanin, besides functioning as a broadband UV absorbent, has antioxidant and radical scavenging properties. […] However, there is growing evidence that the relationship between pigmentation and photoprotection is far more complex than assumed.

Source: The Protective Role of Melanin Against UV Damage in Human Skin in Photochemistry and Photobiology, Volume 84, (3): 539–549.

Although it is known that melanin can very effectively protect against DNA damage from short-wavelength (UV) light, no scientific studies have so far pinpointed the exact mechanisms involved.

Also see : Moles (skin feature)plugin-autotooltip__plain plugin-autotooltip_bigMoles (skin feature)

Benign moles are extremely common on human skin, but their functions (if any) are unknown. There are theories however - the most prominent being that the extra melanin produced in the moles' melanocytes helps to protect against UV radiation. But melanin-rich sites in human skin are often prevalent in areas where sunlight rarely reaches. Further, many nocturnal mammals - bats for example - have skin rich in melanocytes though they are not in any danger from UV in sunlight.

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