This is a list of common skin tones!
To produce the shading colors, duplicate the layer in which just the
base color is on and set it to multiply.
To get the contrasted shading, which is probably a better choice to
use,duplicate the base color layer, desaturate it, and set to multiply.
If you want to get more shades, just keep duplicating the layer that
has the first shading on it. OR just create a new layer and set to
multiply and than color using the base color.