Any time you select a set of paints, you are choosing a gamut or a range of colors that you can mix. There is no magical combination of paint that will enable you to mix every color. For example, you can mix orange from a combination of red and yellow, but the orange mixed with the two paints will not be nearly as saturated as an pure orange paint.
Your choice of paints should depend on your style and subject matter. Figure painters need to be able to mix a range of flesh tones, and landscape painters need to mix greens easily.
Burnt umber is the base for darker skin tones. To that mixture I add cadmium red light and/or cadmium orange along with a some raw sienna. In the shadows, I often add ultramarine blue, perylene maroon, or ultramarine violet in the shadows.
Here is an example of a quick sketch that uses burnt umber, cadmium red light, raw sienna, and ultramarine blue. There may also be some perylene maroon in the shadows.
There are two rules for mixing darks in watercolor. First, use plenty of paint and water, and, second, pick the right combination of paints.
If I have to paint a large dark passage, I will often set out my paints in mixing cups instead of grabbing paint from a palette well. I will use one cup for each single pigment and then let the colors combine on the page.
I squeeze out lots of paint, roughly the same amount I would use if I were squeezing out toothpaste to go on a toothbrush. Then, I add enough water to bring the paint to the consistency of heavy cream. As I am painting the darks, I try never to rinse my brush until I finish the passage.
Just about any combination of red, yellow, and blue will produce a flesh tone in watercolor. Each situation is different and no formula substitutes for your own observation. I will share what works for me.
For average caucasian skin, I use Winsor & Newton Raw Sienna or Yellow Ochre (they're quite similar), M. Graham Cadmium Red Light, and a blue, violet, or (rarely) green, The blue depends on the subject, the lighting, and the pigments I am using in the rest of the painting. Cerulean blue is probably the easiest to work with and works best for light-skinned subjects. Sometimes I use Winsor & Newton Cobalt Blue and sometimes I use Holbein Mineral Violet.
My dog tore up my camera. Sigh. So, recently I have been shopping for a new camera.
When I started painting, I always worked from life. A couple of years ago I realized that working from life, although it is a great way to work, severely restricted the types of poses I could paint. I wanted to paint movement --- crowds of people, skateboarders in mid-air, dancers, and revelers. I bought a point and shoot camera. It worked well enough, but it had some drawbacks. Maybe it was a blessing when Lucy ate my camera because the old camera gave me a chance to learn what to look for in a camera for reference photographs.
Sometimes I want to create sketches at a small scale before do start a watercolor on a large sheet of paper, and I want the proportion of the sketch to match the proportion for the large sheet. Here's a simple calculator that will figure out the dimensions you should use in your sketchbook.
For example, suppose you are planning to do a 22" x 30" painting, and your sketchbook is 8.5x11. Enter the numbers in the form, click the "Calculate!" button, and you will see that you will need to crop your sketchbook page to 8.07 x 11 to keep the proportion the same as your full sheet.
I'm having trouble getting this to work inside the blog. If you're interested, take a look at it on my other website.
I very often hear admonitions about the importance of value in painting. What I hear less frequently, except for advice that preliminary value sketches are helpful, is practical advice on how to go about choosing values. Although I don't have a specific formula for deciding on values, I have accumulated several rules of thumb that are helpful to me.
I had noticed for several months ago that the light and shadow on an object can change very suddenly and dramatically. This phenomenon was especially noticeable around 1:30 in the afternoon. I figured that the sun must shift from the east side of the sky to the west side of the sky around 1:30. My solution was simply to plan for a lunch break around 1:30. Everything worked fine until yesterday, when I was working in the morning and experienced the same sudden shift in lighting. I decided it was time to learn more about exactly how the sun tracks across the sky.