A “How To” Tutorial from NFAC:

WATERCOLOR SKIES

By Phyllis Overstreet

Materials Needed:

• Spiral Notebook/140 W/C Paper (Canson)
• Small Travel W/C Palette W/Brush
• Ultra Fine Sharpie Pen
• 2 Film Canisters Filled With Water
• Folding Stool
Camera

I’ve been asked by students "What shall I do with the sky?" or "What color do I make the sky?" I think the most important suggestion I can give is "Get in with the color on wet paper and get out quickly and stay out until the paper is dry." If you go back in you will probably ruin the luminosity and fluidity of the color moving over the surface of the paper.

Some paintings have the sky as the focal point, such as a sunset, sunrise, approaching storm, etc. These skies should take up about 2/3 of the paper. They should have more contrast of values (darks against lights) richer color, more action.

Some skies only support another focal point, such as a barn, mountain range, lake, etc.
If there is a lot of detail in the rest of the painting, you should keep the sky calm probably using a graded wash.

When doing clouds, you can come back in after the initial sky is dry and delineate some areas of clouds with hard edges. Be careful not to do too many hard edges, most edges should be soft. This means a gradual change of value. Skies are certainly not always blue. Even when there are no clouds a sky can have as many as three colors. A sky is almost always lighter at the horizon getting more color in the upper atmosphere. A winter sky is usually a warmer blue (untramarine blue). Summer sky a cobalt blue and a Spring sky a green blue (thalo blue). The color of the sky is reflected in or on things in your painting. A lake is blue if the sky is blue, gray if the sky is gray, red or orange if it reflects a sunset or sunrise. A metal barn roof can reflect the color of the sky. If the sky is a warm reddish sunset even the trees and mountain slopes reflect that color as well as their local color.
Be sure to practice these and other suggestions many times before you work on the painting you’re doing for a special show. Remember, you have to ruin a lot of paper before you can get the results you want. Of course, you can have a "happy accident" but don’t count on it.

Other tutorials: Travel Journal Sketches