6 : nickel azomethine yellow (PY150), cadmium scarlet (PR108), quinacridone magenta (PR122), ultramarine blue (PB29), phthalocyanine blue GS (PB15:3), phthalocyanine green YS (PG36) Because it provides pure pigment paints for each of the six colors in the secondary color wheel, the secondary palette offers the most evenly balanced and highly saturated range of mixing possibilities of any minimal palette. It is also the foundation of any colorist palette, which attempts to sample the entire range of hues, specifically including oranges, greens and purples, at close to maximum saturation.
Painters who use this palette do not try to split or fix the "impurity" of three "primary" paints; they know that saturation costs are inevitable, not the result of tainted "primary" colors. They just do the commonsensical thing, and add three paints where the "primary" paint mixtures are dullest.
In this way, the secondary palette addresses the four fundamental palette limitations found in the "primary" triad palette:
deep darks Because each color has a matching complement on the opposite side of the color wheel, it is possible to choose one or two pairs of paints as mixing complements, which means dark grays can be conveniently mixed from just two paints.
maximum chroma No other selection of six paints will produce more intense color mixtures around the entire circumference of the color wheel.
pigment variety The large color contrast between all the paints makes it easier to choose paints with texture contrasts as well opaque warm colors vs. transparent cool colors, granulating vs. diffusing, intense vs. dull. This produces considerable pigment variety.
mixing convenience A great variety of color mixtures are possible with just two paints. In the "primary" triad palette, browns and ochres had to be mixed with all three "primaries". In the secondary palette, most can be mixed with the red orange paint and either the blue violet, cyan or green paint. As the demonstration painting shows, the palette can mix a rich variety of maroon, brown and ochre tones.
As Voltaire might say, this is the best of all possible minimal palettes.
There is also no other palette that makes mixing the color circle easier to visualize or teach. There's no irrelevant "color theory" doggerel about tainted "primary" colors, and division of the color circle by six hues is easy for children to understand. By comparison, the split "primary" palette requires three paints for nearly all mixtures, and encumbers everything with pointless sanctions against "crossing the primaries" or "mixing mud".
Finally, the flexibility of the six color or secondary palette appears in the freedom you have to customize the three complementary color pairs yellow with blue violet, red orange with green blue, and magenta with green to suit your needs for a particular painting. This puts the emphasis squarely on choosing paints, quirky and beautiful material substances, to suit the effects you want in a particular painting, rather than focusing always on the abstract realm of colors and fixed color mixing recipes.
The underlying secondary palette structure is always there to keep the basic color mixing relationships straightforward and familiar. The more important consideration is then to select two paints that produce desirable pigment textures and are compatible wet in wet. For example, pyrrole orange and phthalo turquoise mix seamlessly in all situations; cadmium scarlet and phthalo turquoise separate in the mixing well and when applied wet in wet.
Here are my suggestions for paints that make the palette easiest to use:
yellow/blue violet : I prefer nickel azomethine yellow (PY150) because it is so versatile: completely transparent and strongly tinting, with a color that ranges from an ochrish yellow in masstone to a sunny, balanced yellow in tints. Hansa yellow (PY97) is also extremely good, though not as lightfast. Instead, the benzimidazolone yellows (PY151 or PY154) have high saturation, good tinting strength and are completely lightfast hard to beat as basic yellow paints.
If you want to "bias" the yellow toward green (cool), then bismuth yellow (PY184), cadmium lemon (PY35) or copper azomethine yellow ("green gold", PY129) are all excellent choices, though I prefer green gold for its lightfastness, transparency and mixing versatility. I would avoid hansa yellow light (PY3) due to its marginal lightfastness. To bias the yellow toward orange (warm), use cadmium yellow deep or a warm shade of cadmium yellow medium (PY35), hansa yellow deep (PY65) or my favorite, nickel dioxine yellow (PY153).
For the complementary blue violet, ultramarine blue (PB29) is the best choice, though the warmer cobalt blue (PB28), cobalt blue deep (PB72), or the cooler M. Graham ultramarine violet (PV15) or the very dark and unsaturated indanthrone blue (PB60) may be interesting alternatives to enhance the dark/light contrast that is basic to any yellow/violet pairing.
red orange/green blue : The demonstration painting pairs perinone orange (PO43) with phthalocyanine blue GS (PB15:3), but perinone orange is marginally lightfast. Much better red oranges include cadmium orange (PO20) or, for darker mixed grays, cadmium scarlet (PR108). To bias the red orange toward yellow, try cadmium orange (PO20) or benzimida orange (PO62). Slightly cooler red oranges include naphthol scarlet (PR188), pyrrole scarlet (PR255) or the blazing pyrrole red (PR254). (Note that pyrrole orange (PO73), though a gorgeous saturated red orange, paradoxically makes less saturated mixtures with both yellow and violet red than does the slightly less saturated cadmium orange.)
For the green blue paint, the attractive phthalocyanine cyan (Holbein peacock blue, PB17) is no longer available, so the choice for a transparent, strongly tinting and lightfast green blue comes down to phthalocyanine turquoise (PB16) or the typically lighter valued phthalocyanine blue GS (green shade, PB15:3). Cerulean blue (PB35) or a phthalocyanine blue RS (red shade, PB15:6) can be used in place of a phthalo blue, but cobalt paints are lighter valued and relatively unsaturated, which restricts somewhat the mixable range of dark values; cerulean blues are also granulating and relatively opaque. Note that it is possible to get a true neutral (gray) tone through the right choice of orange and cyan (green blue) paints.
violet red/green : There are fewer pigments available for this complementary pairing, although it is possible to get a perfect black mixture with the right choices. The demonstration painting was made with quinacridone rose (PV19) , for the support it gives to very dark red blue and neutral mixtures, and phthalo green YS (yellow shade, PG36) as its mixing complement. But a better choice is quinacridone magenta (PR122) which produces the most saturated purple mixtures with ultramarine blue.
For warmer or darker mixtures, at the cost of duller purple mixtures, quinacridone pyrrolidone (PR N/A) or quinacridone violet (PV19) can be used instead.
These dark red or violet red paints will give very dark, dull blues and violets when mixed with the major alternative green paint, phthalocyanine green BS (blue shade, PG7), which requires a red or maroon mixing complement, such as pyrrole red (PR254) , perylene maroon (PR179) or quinacridone maroon (PR206). Most convenience greens, such as permanent green or hooker's green, will mix rich dark browns or yellow greens with the quinacridone rose/magenta paints, but will only mix true neutrals with a violet paint, such as dioxazine violet (PV23).
Dozens of other variations on this palette are possible: you're free to change any single paint, or any pair of complementary colors, independently of the others. Nor is it required to choose only saturated paints. The red orange can be represented by an "earth" color such as burnt sienna (PBr7) or quinacridone maroon (PR206); the yellow by quinacridone gold (PO49), raw sienna (PBr7) or yellow ochre (PY43); similar substitutions are possible for the green, blue and magenta paints. In this way the chroma range of the palette can be constricted to produce mixtures that are naturally subdued, dark or austere.
A delightfully compact and elegantly designed color tutorial based on the secondary or six color palette is available as Ordering Colors, Playing with Colors by Moritz Zwimpfer (School of Design Basel/Verlag Niggli, 2002).