It's a question I'm asked more than I thought I would be. I assume most are searching for some deep meaning answer like, "I wanted to explore how society views interracial relationships." The truth is I've never viewed Savannah as anything more than a strong female character. Her race was never anything more than a salute to Pam Grier and to a few former girlfriends.
Savannah is African-American because she always was in my mind. That's the answer.