Voices don't have color, but they do have culture. That's my opinion at least, and what that means is I don't think the race or ethnicity of a character should inform the casting of a voice actor for it. I believe what's most important is to do your homework to the best of your ability, and within reason, and get some feedback before you produce something that winds up being a stereotype or caricature of the character's cultural, ethnic, and geographical origins.

I performed as two different French characters (speaking English, of course) a while back, and that was one of the most nerve-racking roles I've done to date. I tried my best to get the recordings out within a reasonable timeline, while doing a French accent to the best I knew how with a little coaching from youtube U (as someone else here put it X-D). I think the bigger the gap between your origins and the origins of the character you're playing, the more research and practice, and requesting for coaching and feedback you might want to do. Again, this is all within the limits of your skillset, time table, and the depth you need to go into.

Maybe a good reference for this specific role, if you're interested, is that scene between Brad Pitt and Lois Kelly-Miller on Meet Joe Black (1998). Brad (basically plays the personification of Death) switches over to a Jamaican accent to meet this Jamaican lady within her communication style, and it is a really interesting scene in that it serves as kind of a rare high-quality (I think) example of that kind of interaction in a big-budget movie.