The inclusion of "face" is a figment of that posters' imagination. It does relate to skin colour though, whether you can extend that to "race" it's an entirely different thing.
You have to remember we (Southern Cone at least) mostly descend from Mediterranean immigrants from the poorest parts of Spain/Italy, i.e. the south, and anyone who has been to Sicily or Andalucia can tell you people's skin isn't precisely "white", nor "black", but the result of centuries of various mixtures between Europeans and the Ottomans/Maghreb.
Skin "tone" would be more precise. Actually, as I wrote this it dawned on me (literally, throughout the entire Suarez saga I didn't notice it even once) that I've spent my entire life calling my brother "Negro". Not consistently, I tend to use his name, certainly do when in the company of others. I'm actualy trying to work out the context I very occasionally use it in and it tends to be when relaxed, alone, but each minding our own thing, if I call him over for a chat, to share a beer, that sort of thing. It's a nothing word really, just call him that because he is the darkest one in the household, both skin and hair, which doubles up. During the Summer people usually mix us up, during the Winter they definitely wouldn't, that's all there is to the "origins" of it.