[Chris Saper]

First, this boy's hair is lit by strong, and very warm direct sunlight, coming from our upper left. The hair on our upper right is also very light, but is only illuminated by reflected blue sky. The dark area on top of the head needs to act as an area of temperature transition. The side of the hair on our right is influenced by the warmth of the sunlight, but is somewhat obliquely positioned, and so registers more accurate local color.

I don't have many colors on my palette, so I mix up neutrals and earth colors. If your palette already has them, you can just go for the color you want.

Colors are:

Permanent Alizarin
Permanent Rose
Cadmium Scarlet
Cadmium Lemon
Pthalo Yellow-Green
Pthalo Green
Ultramarine Blue

Flake White Replacement
Ivory Black

The dark color is a mix of Cad Scarlet, Ultramarine Blue, and little of each of the greens.

The local color is a middle-light value yellow, grayed down with warms. Its a mix of the dark base, lightened and warmed with Cad lemon, white and Pthalo yellow-green.

The cool light is a mix of Ultramarine Blue. white, and Cad lemon.

The warm light is white and a touch of Indian Yellow, which I'll bring out for just such an occasion.