The media wanted George Zimmerman to be white, just like they did with the DC Sniper 10 years ago and just like they did with the Boston Bombing suspects. When it turned out he was hIspanic, they just made him a "White hispanic" and made sure it was a white-black story.
And it's real obvious why: the media doesn't want any friction between blacks and hispanics. They want them to be a lockstep voting coalition in elections. Reporting Zimmerman as a hispanic might cause tension in that coalition.