I first lay in a saturated neutral color as the base for the face. I use little to no white in this process, using a mix of Naples Yellow, Cad Yellow, Cad Red, Cobalt Blue, and Viridian.
At this stage I mixed a new shade of color for the skintone to layout the placement of the shadows on the face as well as laying out the background to aid me in finding both color balance and facial structure of the model.
By this stage I layed in my darkest dark and lightest light and continue to block in midtones whilst building form and structure, paying attention to how each brushstroke correspond with each other to construct a strong and accurate representation of the model. I have yet to use black yet into this stage, mixing my darks with Alizarin Crimson, Ultramarine Blue, and Viridian.
I continue to block in and layer the paint until an accurate representation of the model has been sculpted out from the painting. I used a few small dabs of Ivory Black mixed with Ultramarine Blue and Alizarin Crimson to pinpoint the darkest parts of the model as well as Titanium White mixed with Naples Yellow and Cad Red.