@KurtF, you mean, from light to dark, right? If he painted from dark to light, he would first put down dark values and then use light paint on top of them. For example, in watercolor painting you paint from light to dark, because the paints are transparent and you can't paint any light values once you put down your darker tones. In oil painting, however, you can work from dark to light because the paint is very opaque. Sami Souza is painting from light to dark. It's very obvious in the beginning steps of the face construction.