12 : cadmium yellow light (PY35), raw sienna (PBr7), burnt sienna (PBr7), cadmium orange (PO20), cadmium scarlet (PR108), alizarin crimson (? PR83), cobalt violet deep (PV14), ultramarine blue (PB29), ceruleuan blue (PB35), phthalocyanine green BS (PG7), sap green [hue], payne's gray [hue] This is the "beginner's" or basic palette recommended by Philadelphia painter and art academic Charles LeClair, and it's a well balanced and instructive selection.
The thinking behind the palette design can be analyzed in three steps: first, the decision to base the palette on equally spaced anchor colors; then, to fill in the color wheel by adding paints in the spaces between the anchor colors; and last, to add key convenience paints two earth colors for subdued tones, and a cool, dark neutral (payne's gray).
I interpret the anchor colors as the four artist's primaries in this case, cadmium yellow (PY35), alizarin crimson (PR83), ultramarine blue (PB29) and phthalo green (PG7), although the palette could be based on the equally spaced secondary palette. Either way, the anchor colors form the basic mixing framework and must be chosen carefully:
Red. It is essential to replace the alizarin crimson with a lightfast cool red, such as quinacridone carmine (PR N/A) or quinacridone rose (PV19). Those red tints in the lower left of LeClair's demonstration painting will quickly fade if painted with alizarin crimson. Not only are the quinacridones more lightfast, they're more saturated and equally transparent (in the best brands).
Yellow. Benzimida yellow (PY151 or PY154), the greenish hansa yellow light (PY3) or the radiant and superbly transparent nickel azomethine yellow (PY150) can replace the cadmium yellow; or a cadmium lemon can be used instead. The yellow paint needs to be chosen carefully to get the right range in both orange and green mixtures: cadmium yellows vary from a neutral to a very warm yellow, depending on the brand you choose.
Green. The less saturated but granulating viridian (PG18) has the same hue as phthalo green but is less staining and gives more textural character to green mixtures; the yellower, brominated form of phthalocyanine green (PG38) mixes lighter valued, brighter greens.
Blue. For the "primary" blue, ultramarine blue (PB29) is very hard to beat: it mixes saturated violets and blues, makes radiantly deep skies, and works very well as a cool shadow color. Cobalt blue (PB28) is just as useful, though its neutral mixtures are not as dark. A phthalo blue (PB15) gives luminous blues at moderate dilution, and can be manipulated to produce backrun effects, but its violet mixtures are relatively dull and it lacks pigment texture.
With the four artist's primaries in place, it's easy to select hues to split the color distance between them. LeClair's choice of sap green is very good, but other convenience greens that would work well are permanent green, hooker's green or olive green, depending on your color preferences. The choice of cerulean blue (PB35/36) needs to be made carefully, as the hue and granulation of this paint vary across paint brands. (I would prefer a middle blue, which also tends to be more saturated, because it can be easily pulled toward green by mixing with the phthalo green.) A green shade of phthalocyanine blue (PB15) is a strong alternative, as it takes on a distinct greenish hue in tints. The cobalt violet is mostly attractive for its delicate granulation and its high saturation at light values. Because it is light valued, it can be used to mix a delicate floral color with any rose or magenta quinacridone. Darker violets can be mixed from the ultramarine and quinacridone paints.
Demonstrating again the emphasis most artists place on the warm side of the color wheel, LeClair splits the color span between crimson and yellow with not one but two paints, cadmium scarlet and cadmium orange. These "hot" colors give the palette a warm brilliance and a full range of warm/cool color contrasts. Comparable synthetic organic pigments, such as naphthol scarlet (PR188) and benzimidazolone orange (PO62), would work just as well, and give more saturated tints, though when applied full strength they are about as opaque and staining as the cadmiums.
The two earth colors are used to mute (desaturate) mixtures, and as foundation tints to give a warm background to more saturated color glazes. LeClair probably uses these earth paints a lot, as most of his paint selections are as strongly saturated as possible.
Finally, the dark neutral payne's gray provides a cool shade (I call it "payne's indigo") close to black. Many brands of sepia would provide a warm alternative, and if you're feeling adventurous, indanthrone blue (PB60) makes an interesting shadow color with a very beautiful range of tints. The dark neutral is the color to use to mix the saturated colors into darker tones and shades, and to mix dull greens with the yellow ochre and cadmium yellow.
Quibbles over specific paints aside, the color spacing of LeClair's palette has a lot to recommend it. It uses as many paints as a tertiary color wheel, but through judicious spacing of colors around the hue circle, LeClair can add two earths and a dark neutral to the range. These are very convenient colors to have, and make this palette an excellent step up from the very compact secondary palette. (See also the basic palette for another example of the palette design logic explained here.)