A useful core palette needs enough range to mix blues, greens, oranges, violets, neutrals and darks without carrying a separate paint for every subject. Eight positions make a balanced starting system.
At a glance
Start with eight roles, not eight products. Choose two blues, two yellows, two reds and two earth colours.
Bias matters. Warm and cool versions of each primary make cleaner secondary colours possible.
Know the limits. A palette without a cool red struggles to mix clear violets; one without a cool blue struggles with bright greens.
Prefer pigments you can identify. Single-pigment watercolours make the behaviour of a mixture easier to understand, but the full label explanation belongs in the pigment-code guide.
Add a colour only for a job the palette cannot do. If the result can be mixed from the colours already there, another tube adds duplication.
The eight palette positions
A warm blue such as French Ultramarine, PB29, supports violets, subdued greens and many neutral mixtures. A cool blue, often from the phthalo-blue family, opens brighter greens and deeper cool mixtures.
A warm yellow supports oranges and warm greens. A cool yellow leans towards green and helps produce cleaner, brighter greens. Exact colour names and codes vary between makers, so choose by mixing role and confirm the label.
A warm red supports oranges and warm mixtures. A cool red, often a rose or magenta-leaning pigment, is necessary for cleaner violets and purples. This is the position missing from many over-restricted palettes.
Two earth colours complete the system. A yellow earth gives muted warmth. A sienna or umber gives a useful red-brown or cool brown for neutrals. Burnt Sienna is not one fixed pigment: formulations may use PR101, PBr7 or mixtures, as explained in the earth-pigments guide.
What the palette needs to do
Test the system by mixing the secondary colours you actually use, then a range of neutrals and darks. The point is not theoretical completeness. It is to cover the work you make without leaving obvious gaps.
If clear violets consistently fail, inspect the red and blue biases before buying a premixed violet. If greens are always dull, inspect the cool yellow and cool blue positions. If darks feel flat, test different proportions of a blue and an earth colour before adding black.
Practical test
The test for adding a colour
Ask one question: can the required result be mixed from the colours already here?
If it can, another tube probably adds duplication. If it cannot, and that result matters repeatedly in your work, the colour has a defined role. A convenience green for frequent landscape work, a violet with a particular behaviour, or a granulating colour for texture can all earn a place this way.
Building from six to ten colours
Six split primaries form the colour-mixing core. The two earths bring the working palette to eight. A ninth or tenth colour should answer a repeated need rather than broaden the collection without purpose.
This structure is deliberately format neutral. Once the colours are settled, the guide to half pans versus tubes helps decide how to carry and use them.
The practical verdict
A core palette is a system of roles. Begin with six split primaries, add two useful earths, and learn where the system succeeds or fails on your own paper. Expansion should follow evidence from the work, not novelty in the paint range.