The social construction of mixed race
I have a question I was pondering earlier today -- what makes someone "mixed race"? The easiest comparison is between Colin Powell and Barack Obama. I'm so used to hearing about Obama being "mixed race" (often by people with a race-baiting agenda) but then he's also routinely described as "black". Whereas Colin Powell probably has a greater percentage of European ancestry than Obama, but I've never heard his race described as anything other than "black".
What I'm wondering is if my hypothesis is correct that "mixed race" seems to exclusively be applied to people with a white parent and a black parent -- that folks who have been "mixed" going back more generations just tend to get lumped in with the "black" category. Does that describe how race is generally constructed, or is that just something I came up with on my own?