This morning I watched the portrait video of Mary Whyte painting a young man wearing glasses at artworkshops.tv. She starts with a drawing that shows the shapes of the different areas within the face - the shadows, the highlights and lights, with the rest of the area being the mid-tones. She said she always starts her paintings from the top, working her way down. As a base for shadows, Ms. Whyte laid in ultramarine blue then immediately dropped in red tones. Wonderful, at least when she does it. I tried that with the forehead area and it doesn't look too bad IRL but it will require more value structure.
The dark background is painted with Perm. Alizarin Crimson, Indanthrene Blue, Hookers Green, Fr. Ultra. Blue, and Raw Sienna, tying the background colors into the darks of the blue hat the man is wearing. I wish my camera would pick up the colors in the background instead of seeing mostly blue.
My goal was to paint one small area at a time, leaving some white shapes. I can see at this stage that I'm not achieving my goal very well, The reference photo shows light on both sides of the face with the shadows down the middle (backlighting). Will be quite interesting and challenging to paint this.
Another portrait video I watched at artworkshops.tv was by Jean Pederson. A wonderful video, chock full of information. Ms. Pederson also does a detail drawing (map) of the face. Both of the videos mentioned here are well worth watching if one wants to learn more about portraiture and watercolor.