Hi I wanted to post a quick portrait demo showing a relatively painless approach to portraits using a limited palette and 4 values.
Here's the reference borrowed from the RIL. Thanks to the contributor!:
I painted a 4 value study using only black, a dark grey, a lighter grey, and white.
(In the following post I'll show an easy method for creating the 4 value study. )

I let the 4 value study dry.
Using a limited palette of alrizarin crimson, cad yellow, ultramarine, white, I mixed a generic overall pinkish flesh tone and diluted the paint with water and lightly tinted the entire face, except for the white areas. The key is to paint transparently as if you are tinting a photo. You can dilute your acrylic paint with medium or water. Saturation is automatically controlled by the fact that the paint is diluted and the pigments are dispursed sparsly and the grey underpainting is showing thru and influencing the color. I used the yellow to mix a light color and painted the lights on the sides.
Finally, I mixed and added little saturated areas of local color, mixed with the three primaries. The key is restraint. If the color is too strong, just glaze it with the generic flesh tint you already mixed. Mix a brown with red, yellow, and a little black to strengthen the shadows. Add warm and cool greyed colors where observed. I tinted the hat, shirt, and suspenders with ultramarine and a little cerulean. The whole 5x7 portrait took about 90 minutes. The grey underpainting really helped hold it together. After that first flesh tint is added you can get really reckless with the color and it will still read ok. It's not a great portrait or anything but fun, consistant, and relatively painless, compared to some of the other approaches out there.
