It's long been established that somebody who is 1/4 black is black. Except if he's conservative.
Zimmerman's grandmother was Afro-Peruvian (one-half black). The media wanted him to be a Southern white racist, so that's how he was initially portrayed, and that could be how the jurors think of him.
“Except if he’s conservative. “
From what I’ve read, Zimmerman is a democrat.