Whenever you come up with a word that describes a particular group of people, someone is going to use it as a term of abuse. There are plenty of abusive terms for people of African origins. In June 2008, it's acceptable to call people black, but it's not acceptable for an English speaking white person to use the Spanish word negre - however it's spelled. Calling them coloured is currently out of fashion, but it's OK to call them "people of colour". The word doesn't matter. What's important is whether you respect the person. It would be just as abusive to complain about those Afro-Caribbeans coming over here etc etc.
About 30 years ago, when I was a youth worker, Roots was on TV. The black kids in my youth club thought it was hilarious when an elderly white woman in the programme described a black woman as a "darkie", and I used the word for some time afterwards when I needed to ridicule the racist attitudes of some of the white parents. However, a few years later "darkie" went back to being a term of abuse.
The interesting thing is that "white" people are pink and "black" people are brown. I've only once met someone with really black skin. She was a nurse from Ethiopia and she was gorgeous.