I'm not scared of painting over existing color(s) anymore and found that painting the entire canvas first, in this case Liquitex Unbleached Titanium, helps the painting look better in the long run. I gave this canvas about four coats.
Initial black and white outlines of the illustration using Liquitex acrylic paint markers on top of four coats of Unbleached Titanium.
The black outlines have been expanded inward 1/2" inch with a thin tip Liquitex Carbon Black acrylic paint marker, then filled in the rest of the way with brushed on Mars Black paint. Carbon Black, by the way, is more like an ink than a thick bodied paint, so I always end up getting my lines set up with the marker, then carefully going over those lines later with Mars Black brush paint. Since the Mars Black went on over top of another color, it required two coats for really nice coverage.
The white outlines have been thickened on each side with a Liquitex white acrylic paint marker, then filled in with brushed on Titanium White paint. Six months ago I would have stopped here and called the painting done. Also, I would not have used white paint for the outline, it would have remained unpainted canvas.
Always the scary part: Adding color to the face, I start on the edges and paint inward using Liquitex Cadmium Red Medium Hue and a smaller angled brush. Instead of applying paint from a palette, I simply applied it right from the tube onto the canvas. A thinner coat will go on afterwards.
The finished painting, which I'll call Bad Boss as it hangs in my house. This painting was completed in less than a week.