What causes the pigmentary changes of the skin seen in chronic renal failure?

It is the result of increased amounts of melanin present in the basal layer of the epidermis and superficial dermis. It has been proposed that such patients have decreased metabolism of b-melanocyte–stimulating hormone (β-MSH) by diseased kidneys, leading to elevated plasma levels of b-MSH, a hormone that stimulates melanocytes to produce more melanin.