Vitamin D, produced by skin exposed to sunlight, protects against several forms of cancer. Melanin in the surface layers of the skin blocks penetration of sunlight, reducing vitamin D production.
Black people in low-sun environs are normally vitamin D deficient - which causes a variety of problems, including increased incidence of several kinds of cancer.
White people in high-sun environs suffer too much damage from irradiation to be repaired, even with the saturated vitamin D production to counter.
White people are adapted to low sun production of vitamin D. Black people are adapted to high-sun protection from UV damage.
But isn't that association with colon and prostate cancer rather than skin cancer?