3 : yellow ochre (PY43), burnt sienna (PBr7), ultramarine blue (PB29) Although this palette sometimes goes by the name "Velázquez palette," it is not a palette characteristic of Velázquez, and it was used centuries before his time. The Roman naturalist Pliny the Elder describes the Greek painter Apelles (c.370 BCE) using a palette consisting only of "white from Milos, Attic yellow, red from Sinope and the black called atramentum" that is, lead white, yellow ochre, red ochre and carbon black, black standing for all "cool" pigments. The Altamira cave paintings of 15,000 years ago are rendered in carbon black and red ochre on yellow limestone walls.
The original version of this palette used lamp black (PBk6) or ivory black (PBk9) for the dark values, and the red and yellow iron oxide pigments for hue variety. In oil or encaustic painting, an unsaturated green is available by adding a touch of black to the yellow ochre, and a convincing blue can be made from black properly mixed with or glazed over white, providing a hue range deficient only in purple.
The palette with ultramarine blue is probably the most dramatic of the "minimal" or three paint palettes; it produces an amazing range of color mixtures. Ultramarine creates delightful pigment textures and shadow darks when mixed with burnt sienna, and diluting these mixtures creates a variety of pearly, fleecy wash textures. By itself the burnt sienna appears rather red, and mixtures with yellow ochre blend into dry grass, which grows green with a slight touch of ultramarine.
My favorite alternative to the overly chromatic ultramarine blue is iron blue (PB27), which increases the green in all mixtures, producing cooler near blacks with burnt sienna and significantly more pronounced greens with yellow ochre. I find it is necessary to accent the red side of the color range to compensate, choosing instead of burnt sienna paints such as light red, venetian red (PR101) or even chrome aluminum stannate (PR233). These paints increase the hue range on the red side and a completely new range of textures and color mixtures with iron blue.
Another, even more restricted variation on this palette uses burnt umber in place of burnt sienna, raw umber in place of yellow ochre, and payne's gray for the dark. This is particularly challenging to use, but creates interesting still life, portrait or landscape paintings under cool light and an overall effect that is close to a sepia wash drawing.
I have been emphasizing the hue contrasts produced by different palette choices because these clarify the gamut limits of the palette. But value remains the fundamental design resource, now coupled to differences in the relative warmth of color mixtures along the warm/cool contrast. This palette reduces design problems to variations in light/dark and warm/cool, as all hues are muted and some hues (carmines and purples) are missing entirely.
A great way to start with this palette is to use only burnt sienna and ultramarine blue. These two paints alone, across the full range from masstone to tint, mix a remarkably evocative range of colors a furzy tan, ripe orange red, deep brown, granite gray, jet black, indigo, a deep dark blue and a cool sky blue. J.S. Sargent and William Russell Flint were masters at pulling the full range of possibilities out of the combination of these two paints.
Once you feel comfortable using these two colors, add a yellow such as yellow ochre (PY43), raw sienna (PBr7), or a greenish raw umber (PBr7). Depending on the specific brand of watercolors you use, it's possible to get a mossy green as well, essentially completing the color circle.
The Velázquez palette lets you concentrate on very subtle mixing variations, since you must get all your color effects with minimal materials. Without the overwhelming distraction of the hundreds of possible combinations among a dozen or so paints, the painter more quickly improves his sense of color harmony and the unexpected eloquence of subtle gradations in muted statements.