Minimal palettes

Palette is also the term for a specific selection of paints (or "colors") and, as a matter of economy, convenience or technique, painters have often preferred palettes comprising the smallest practical selection of paints. Many professional watercolorists work routinely with a palette of a dozen or fewer paints.
Though commercial watercolor brands offer selections of up to 100 or more paint colors in tubes, subtractive pigment mixtures can produce a complete range of colors from a small number of specific paints. In the 19th century a six paint "split primary" palette became popular and is still advocated by older painters. It is based on the three subtractive primary colors (red, yellow and blue), each in a "warm" and "cool" version:
"cool" yellow: Cadmium Lemon (PY35) "warm" yellow: Cadmium Yellow Medium (PY35) "warm" red: Cadmium Scarlet (PR108) "cool" red: Quinacridone Carmine (PV19) "warm" blue: Ultramarine Blue (PB29) "cool" blue": Phthalo Blue (Green Shade) (PB15) The reason for this intricate selection was that bright or saturated mixtures were only produced by related primary colors, e.g. the brightest orange is the mixture of a yellow with some red in it (warm yellow) and a red with some yellow in it (warm red); the brightest green is the mixture of a yellow with some blue in it (cool yellow) with a blue with some yellow in it (cool blue); duller mixtures are produced by mixing contrasted primaries, and the dullest mixtures by mixing three primaries.
The modern approach (the hexachrome palette) also relies on six paints, but spaces them more equally around the hue circle so that their mixtures automatically produce the most saturated color in every hue:
yellow: Cadmium Yellow Pale (PY35 or PY37) or Benzimidazolone Yellow (PY151 or PY154) red orange: Pyrrol Orange (PO73) or Cadmium Scarlet (PR108) magenta: Quinacridone Magenta (PR122) or Quinacridone Rose (PV19) blue violet: Ultramarine Blue (PB29) cyan: Phthalo Turquoise (PB16) or Phthalo Cyan (PB17) green: Phthalo Green (PG7 Blue Shade or PG36 Yellow Shade) Both palettes obtain dull or darkened colors, including a "neutral" (dark gray or black), by mixing together paints or colors on opposite sides of the hue circle -- especially orange or scarlet with cyan, and carmine or magenta with green.
As a matter of convenience, painters typically also add one or more paints made with an iron oxide pigment (the so called "earth" pigments, many of them manufactured as concrete colorants or wood stains) and sold under the names yellow ochre, raw sienna, raw umber, burnt sienna, burnt umber and/or venetian red. Exactly the same brown or ochre colors can be matched with either of the six paint palettes, but it tedious to do. As dark colors also require inconvenient mixing, most painters prefer to add a premixed dark neutral paint containing a carbon (black) pigment, usually sold under the marketing names indigo, payne's gray, neutral tint or sepia.