Painting Dark Skin Tones in Watercolor

Painting skin tones don't have to be complicated. Using a limited palette of a yellow (quin gold), a red (quin magenta) and a blue (Prussian) can create beautiful vibrant clean skin tones.  After you complete your sketch, start with wetting your paper until the shine is off and then take a med. wash of yellow and touch your paper. Use the wetness of the paper to assist in letting your colors flow. Keep the edges against the white highlights clean and soft. I don't use masking fluid anymore, for the tiny highlights, I will come back in at the end of the process with a white pen and add them back in.  

Let your layers dry in between as to not muddy your piece. work in small sections and build up the variations in the skin. 
Don't get hung up with details. The best watercolors are ones that "suggest" or create intrigue. It allows the viewer to add his/her own interpretation of what is happening in the piece.