The six tubes
A split primary palette gives you a warm and a cool version of each primary, and between them they will reach almost anything a photograph asks for. The reason it works is that every primary leans one way or the other, and mixing two that lean towards each other gives a clean secondary while mixing two that lean apart gives a muted one. Having both versions means you can choose.
- A cool yellow, such as lemon yellow. Leans green.
- A warm yellow, such as cadmium yellow deep. Leans orange.
- A cool red, such as quinacridone magenta or alizarin. Leans violet.
- A warm red, such as cadmium red light. Leans orange.
- A cool blue, such as phthalo blue. Leans green.
- A warm blue, such as ultramarine. Leans violet.
Add titanium white. Skip black at the start, because a black mixed from your own blue and red will sit inside the painting in a way that tube black does not.
Mix in the order the painting needs
Do not work down the legend from number 1. The legend is ordered by the engine, not by the painting, and mixing in that order means making 24 small piles with no relationship to each other.
Work by family instead. Find every colour on the legend that belongs to the sky, mix the darkest of them first, and then reach the lighter ones by adding white to what you already have. You will make five related colours from one mixing decision, and because they came from the same parent they will belong together on the canvas.
Then move to the next family. Foliage, skin, stone, whatever the picture is made of. Six or seven families usually cover a 24 colour legend, which turns 24 mixing problems into seven.
Matching without chasing
Put a dab of the mix next to the printed swatch and look at them with your eyes half closed. Squinting removes hue information and leaves value, and value is the part that has to be right. A mix that is a little off in hue and correct in value will disappear into the painting. A mix that is exactly the right hue and one step too light will stand out from across the room.
Accept close. Chasing an exact match wastes paint and produces a mix that is muddier than the one you started with, because every correction adds a third and fourth pigment. Two pigments and white is a clean colour. Four pigments is mud, whatever the swatch says.
Some colours on a legend cannot be reached from six tubes, and the honest thing is to know which. Bright violets, intense oranges and anything fluorescent are outside the range of most split primary sets, and if the picture depends on one, buy that tube rather than mixing towards it for twenty minutes.
Keeping the palette alive
Mix more than you think you need. Running out of a colour halfway through a region is the commonest reason a painting develops a visible seam, because the remix is never quite the same and the join between the two is permanent.
For acrylics a sealed palette with damp paper underneath will keep mixes usable overnight. Oils stay workable for days on a glass palette and can be scraped into a small pot. Watercolour is the exception, since a dried pan rewets to roughly the same colour, which is one of the quiet advantages of the medium for work like this.
Photograph the palette next to the legend before you start painting. If you do have to remix, the photograph tells you what the colour looked like when it was right.
Or ask for fewer colours
Everything above is easier at 12 colours than at 24, and at 12 you can lay the whole palette out before you begin and it will still be usable two hours later.
The number on the guide is a decision about how you want to spend the evening. It is worth making that decision deliberately rather than accepting the default and discovering it at the palette.