Foundry has several packs of figures suitable for an African slave revolt scenario.

Some of the characters could be pirates, but as they are armed with muskets the seem better suited for a land encounter.

But how to paint the skin?

All black is too harsh. All brown is a bit better perhaps, but still not quite right. Searching around the web, I found several good articles. Perry Miniatures blog hs an article titled Painting African skin--the focus, as you might imagine, is Perry's Sudanese.

THe Cool Mini or Not forum has an incredible article covering all ethnic skin tones. The author has collected sample photos, make color swatches and Vallejo paints. Referencing a commercial paint line is not optimal, but I also found, at another location a paint color cross-reference chart. That's still a little sketchy, as I like to use artist's colors. I find that something like Ogre Brown is simply Burnt Umber.

Finally, from Boardgamegeek, a post that gives a simple formula:

Depends on which shade of black you want to render...
I work typically as follows:
basecoat : mix pale flesh + earth brown
wash 1 : mix earth brown + dark red
wash 2 : dark brown
wash 3 : black (only in deeper recesses)
highlight/drybrush : pale flesh (light-handed)
Then sometimes an overall brownish glaze to equalize the tones.

I don't know what the painters for Foundry used, but the results look pretty convincing.