I really wanted to cover texture creation in Zbrush, to paint my character heads. I sourced a number of useful skin textures, and facial photographic reference, then imported them into Zbrush. Loading the textures into the Spotlight tool overlays them on top of the model in the viewport. By transforming (scale, rotate, move) both the image and the underlying model it is possible to line up the image with the geometry below. Using a brush tool and painting over the texture projects the colour information onto the model.
I continued to paint each major facial structure, moving the image when necessary to achieve the best fit for my model. To fill any areas of back facing geometry I used a colour spray brush to sample the nearest colour to the unpainted area.
Using different textures can lead to a mosaic effect due to the variation of lighting and skin tones in the images. I used the clone and smudge tools to subtly blend these border areas together.
The final head looks impressively realistic.