Technically it's a poor argument. If you remember the years of the "one drop rule" in this country, he would historically be listed as "black" or "colored."
"Despite this holding, the one-drop theory is still influential in U.S. society. Multiracial individuals with visible mixed European and African and/or Native American ancestry are often still considered non-white, unless they explicitly declare themselves white or Anglo (this used to be called "passing), and are typically identified instead as mixed-race, bi-racial, mulatto or mestizo, or Black or American Indian, for example. By contrast, these standards are widely rejected by America's Latino community, the majority of whom are of mixed ancestry (usually Amerindian and white, but for whom their Latino cultural heritage is more important to their ethnic identities than "race." The one-drop rule is not generally applied to Latinos of mixed origin or to Arab-Americans.
From Reconstruction until about 1930, the children of black/white interracial parents and of mulatto parents were usually identified as mulatto. It is becoming increasingly common for people to identify themselves as multi-racial, bi-racial, mulatto or mixed, rather than as black or white. The fraction of mixed children census-labeled as solely black dropped from 62% in 1990 to 31% in 2000 (when multiple "races" were first allowed), suggesting that the one-drop theory and denying one's European ancestry and no longer accepted the way it used to be.
http://en.wikipedia.org/wiki/One-drop_rule
There are very few "African Americans, save those of recent immigrant parentage, like Colin Powell, who do not have significant amounts of "white" ancestry, and often some American Indian as well, both from pre Civil war times and from places like Oklahoma, where many former slaves settled and got it on with the locals from various Indian nations. (Whites were doing the same at the same time of course).