Razib at gnxp uses the word “pleiotropy,” but you can focus on its result: “side-effect.” It appears that skin and hair color evolved later than the founding of the major continental racial populations. More on that is availabl in The Blank Slate (see also my notes). However, this ironically implies that skin-color-differences may not be skin deep. Because only a few big mutations seem to cause the change in color that we see, which iplies there was strong selection in favor of light skin color, there may be side effects of this.
Gene Expression: Beware the dark-eyed
The fact that blondes have more fear and redheads feel more pain might make some more sense. Skin color seems to have gotten lighter over the past 5-20 thousand years across northern Eurasia by substitutions and changes in frequency on a few loci of large effect. Evolutionarily this predicts that pleiotropy will product side effect phenotypes before modifier genes can arise to mask the deleterious byproducts of said evolution.
More research still needs to be done, but the great strides that genetic research is making keeps impressing me.
If knowledge is the heart of quality control, we are well on our way to a population with quality.