The General Social Survey data from 2012 are up online. A new question has the interviewer rate the respondent's facial skin color from lightest to darkest on a 10-point scale. To get decent sample sizes, I lumped the lighter together (1-5) and the darker together (6-10). The GSS also has a 10-word vocab test which serves to measure IQ.
The blacks who have lighter skin tones average 5.7 words correct, while the darker ones average 4.6 words. This difference works out to 0.54 standard deviations, or about 8 points of IQ. Those who scored 8 words or more out of 10 made up 15% of light-skinned but only 6% of dark-skinned blacks.
Whites average 6.3 words, so light-skinned blacks are closer to whites than they are to dark-skinned blacks in intelligence. Hence why those with light skin suffer such constant teasing, hounding, and ostracizing from the dark majority of blacks.
We can extrapolate these results to see a future where light-skinned blacks form their own ethnic group and culture, although that may be centuries away. Yet the fundamental split is already visible, as it were.
GSS variables used: wordsum, ratetone, race