They were about 14% in the 70s. But two main things have occurred. First, half of all black children conceived are killed by abortion. (See Black Genocide.org) Second, the Hispanic population has a higher live birth rate than the black population. The 14% figure has slowly edged towards 12% in the last 30 years.
The Census Bureau put the percentage of the population which is black at 12.7% in 2000 and 12.8% in their July 2006 estimate. The highest percentage was the first census, in 1790, when black people were 19.3% of the population—that had dropped to 9.7% in 1930 after the decades of massive immigration from Europe.
Tomato lover, see post 32 for more information.