The white overseers charged with whipping slaves were known as "crackermen," hence "cracker."
I've seen the prefix "Afro-" used like this before, in the same fashion as "Euro-" (eg. "Eurofighter, Eurotunnel"). For example, There's a longstanding black newspaper in DC called the Washington "Afro-American." I believe that the term was more common in the early-to-mid 20th century, before becoming associated more with hairstyles in the '60's...