I'm going to shoot a close-up of a rap artist from Africa. Very dark skin. I want the effect of a spotlight hitting his face/head from about 45 degrees from the camera and a few feet above. Kind of stark. Little or no background seen, and neck/shoulders barely visible.

So the way I imagine it, it's using a key light and nothing else. The question is, should I add a fill that's just strong enough to take the other side of his face out of shadow? Anything else?

I find that a blue backlight looks very good with dark skin...

Can't really tell for sure until you start lighting it but I'd be ready with a small fill and bounce if needed. I would also have a small light and C-stand with grip arm on hand in case you decide you want a hair light to really give a little rim around the top of the head.

Are you going to be shooting it in a dark studio?

It will actually be in a conference room with off-white walls. The opposite wall has 2 windows with blinds that can keep out almost all of the daylight.Any lights I use will be 5600K, so I can easily use the natural light if it helps.

My personal preference would be to go for blue highlights as well. It is a good look, maybe a bit commonly done these days but use what is proven good. I would be inclined to make the backdrop as dark as you can, and maybe throw some dark blue or dark orange patches on it. I think the make-up people do water or oil shine to look like the sweat of energetic performance to also bring out facial highlights. I would take care not to use a wide angle lens a confined location may force you to think of using. For close-ups it may be less than complimentary.

That is my personal preference. I am in no way qualified in this game so please take the advice of others.

I recommend you add some fill. Lighting all of your subject will let you expose for a lit subject that is brighter than the background. This means the background will expose darker which is what you want. If you don't add fill then that side of your subject will be the same exposure as the background. Fill and hair lights will let you separate your subject via exposure. You can dial down the aperture to darken the background because you have raised the level on your subject.

Also, daylight through a window that's bounced around a room is not going to be 5200K. It's like the shade which is typically 3900-4500K depending. A little orange on your lights will help bring it into that range.

Very good ideas here.

I was actually thinking of adding some blue light to his face. Is there anything to know about colors interacting with dark skin vs light skin?

Using a shiny reflector (mylar-type finish) delivers good results on black skin. Large softboxes or white bounces can result in a flat, patchy look as the skin will reflect those as the white sources that they are. I don't use a full gold reflector myself but that look is flattering (it was done a lot in The Help).

My lucky day -- I happen to have a gold reflector!