Flux can do colored skin to some degree, but it struggles with both consistency and "black, white, yellow" or other descriptors that are used for non literal skin tones.

Tried to put as many colours into the training data as possible.

fantasyskincolor, a woman with white|red|blue|green|black|grey|purple|orange|maroon|cyan|teal|pink|ochre|liliac skin

If you do "white" or "black" skin, the subject will have caucasian or african features, so giving the subject a specific ethnicity will fix this.