IQ rises with lighter skin among blacks: Black Americans have an average of about 20% Caucasian ancestry with evidently wide variation, and skin color is a crude index of how much of this ancestry an individual has. General Social Survey interviewers judged their black respondents on skin tone, ranging from "very dark brown" to "very light brown." Participants were also given a vocabulary test, where scores ranged from 0 to 10 correct. This variable serves as a simple measure of IQ. I transformed test scores into IQs (setting the white mean at 100), and these are the averages:
Very dark brown 87
Dark brown 84
Medium brown 90
Light brown 93
Very light brown 91
The extremes have small sample sizes. If we drop those, we see a clear pattern of rising IQs with lighter skin color. The modal category is "medium brown," and this group's IQ is probably higher than the 85 IQ usually seen in IQ studies due to the fact that verbal IQ tends to be higher than math IQ among blacks.
Skeptics will argue that these numbers reflect the greater educational opportunities given to light-skinned blacks, but when a white guy sees someone with characteristically black features, he thinks "black person" not "light-skinned black person."