I actually know of a few dolls of mixed/other/non-caucasian race- but mainly in resin (I have a Nifer by BJTales for example, who is gorgeous) and then there are a LOT of fantasy colours and other humanoid-species entirely.
When it comes to Porcelain the most readily available slip is white. I know artists often have trouble mixing decent flesh tones, even pale ones, so many will make dolls from a variety of races but all in the white porcelain, then blush them or paint them with darker eyebrows, etc, to get an ethnic look. For example, even though Marina (Enchanted Dolls) made a few dark skinned dolls early on, all her recent ethnic dolls, even the Indian and South American inspired ones have been cast in the white porcelain.
I didn't know that about Enchanted Doll! Which dolls are you referring to?
Here are some of the dolls that seem to be referencing cultures or characters of darker skin or ethnicity. I haven't included her Arabian dolls like Makhdot, Scheherezade or Dunyazade.
I have a doubt... when you used colored porcelain.. how is the color evolution? (example: in color of slip, color fresh casting, color in greenware, bisque and mature porcelain?) the color of final porcelain... is more like slip? or like greenware? more lighter? more darker? (questions questions questions...