Many purests will tell you never to use secondary or intermediate colors from tubes when mixing watercolors. Instead, you should always mix your blacks, neutrals (browns) and grays from primary colors. Phoenix artist Julie Gilbert Pollard recommends choosing a selection of watercolors that are mostly warm and cool versions of the primary colors, with no greens or earth colors among them when setting up your palette. Greens in particular are easier to use and often more beautiful when mixed from yellows and blues rather than squeezed from a tube. Grays and earth tones can also be easily mixed with watercolors. These subdued colors will have much more liveliness and beauty than a gray or brown that comes from a tube.
You don’t have to subscribe to this principle yourself, but it is a good idea to practice and experiment with mixing watercolors. The more experience you have with the way color and paint behave, the better your paintings will be.
Here’s more, from Julie’s Watercolor Unleashed (download now at NorthLightShop.com).
Mixing Watercolors: Brown
Brown is really a neutralized version of orange. Begin with orange paint (yellow mixed with red), then add blue. Experiment with various mixtures of different reds, yellows and blues. Cerulean Blue is an inherently light color–you cannot achieve a dark brown with it. Choose a darker blue, such as Ultramarine Blue or Antwerp Blue, when dark browns are needed. The possibilities are infinite, and each combination will yield a unique brown.
Mixing Watercolors: Gray
Begin with blue, then add red and yellow. (Or a very orangey red or orangey yellow.) Again, experimentation is key here, as each will yield different results.
Mixing Watercolors: Black
Proceed with caution when using black, since the color can look dead in a watercolor. It’s usually preferable to use beautiful, clean darks. However, Permanent Alizarin Crimson mixed with Phthalo Green will yield a true transparent black. Use it sparingly.