Single-pigment watercolours contain exactly one colourant, identified by a Colour Index code printed on the label. When paints mix badly and produce colours that are dull or muddy, the problem is usually too many pigments meeting on the paper at once. Knowing which paints are single-pigment, and why that matters, resolves most mixing problems before they happen.

What single-pigment actually means

A single-pigment paint carries one Colour Index code. A multi-pigment paint carries two or more. "PB29, PR101" on a label means two pigments, not one.

The colour name gives you no reliable information about what is inside. Burnt Sienna, Payne's Grey and Sap Green are convenience names that different manufacturers can produce from entirely different pigments. Two tubes labelled Burnt Sienna can behave very differently on paper because one uses a natural earth pigment and another a synthetic iron oxide. The code is the only consistent identifier.

This page is about what the code means for your mixing. For the full explanation of how Colour Index codes are built and how to read them, see what pigment codes actually mean.

Why single-pigment paints mix more cleanly

Every pigment carries its own characteristics: transparency or opacity, granulation tendency, staining behaviour, and the position it occupies on the colour wheel. When you mix two paints, you combine the characteristics of every pigment present.

A paint carrying two pigments, say a convenience orange built from a yellow and a red, brings both into any mix you make with it. Add a blue to darken it and you are working with three pigments at minimum. If the blue is itself multi-pigment, you may have four or five. Every additional pigment introduces another set of optical interactions, and the cumulative effect is a colour that moves towards grey or brown rather than the subdued tone you were aiming for.

Single-pigment paints do not remove this entirely. A mix of French Ultramarine (PB29) and Burnt Sienna (PR101) still involves two pigments. But those interactions are known and predictable. You can test them, remember them and repeat them. Multi-pigment convenience colours introduce variables you may not know are there.

The practical test is simple. Mix two colours together on scrap paper and let them dry. If the result looks like a version of one of the original colours, or lands where you expected on the colour wheel, the mix is clean. If it looks grey or brown when it should not, one of the colours is probably a multi-pigment mix containing a pigment that is fighting the other.

Where single-pigment paints matter most

Not every colour family offers the same choice. Blues and earth colours are well served by single pigments. Greens and oranges are harder, and the options vary from one manufacturer to the next. The positions that matter most are the ones you mix from most often.

A limited palette built around single pigments might include three colours:

A blue. French Ultramarine (PB29) is the standard choice. It is transparent, granulating on some papers, and useful for mixing darks. Phthalo Blue Green Shade (PB15:3) is the colder, higher staining alternative.

A yellow. Hansa Yellow Medium (PY97) is one of the cleaner mixing yellows, transparent and warm without pulling towards orange too quickly. Not every manufacturer offers it under that name or at all, so look for a single-pigment yellow in the same position rather than a particular label.

An earth colour. Burnt Sienna as PR101 mixes cleanly with most blues to produce a wide range of neutrals. The same code can appear under different colour names, which is another reason to read the label rather than the name.

These three form the backbone of a palette that can produce a wide range of colour through mixing. Whether they come from one maker or several, what matters is that each tube carries one code.

A brief reminder on reading the label

On artist grade tubes the code is usually printed in small type on the side or back label. A second code means a second pigment. If the label is hard to parse, the manufacturer's own product page lists the pigment composition, and it is more reliable than a retail listing. Where the two disagree, the manufacturer's page takes precedence.

Student grade paints sometimes carry this information and sometimes do not. The distinction matters most for paints you use in mixes rather than straight from the tube.

The full system, including how the letters and numbers work, is covered in what pigment codes actually mean. For wider context on paper, brushes and related decisions, see the watercolour materials section.

Where multi-pigment convenience colours are still useful

The case for single-pigment paints is not a case against convenience colours as a category. Some multi-pigment mixes behave well and serve purposes that single pigments cannot.

Payne's Grey is a reliable example. Few if any single pigments produce that particular cool, blue-leaning grey, and for painters who use it often, a well made convenience mix saves time without producing unpredictable results, particularly when used as a wash or flat colour rather than as a mixing base.

Convenience greens are another case. Sap Green as a colour name appears on tubes containing anything from a single pigment to several combined, depending on the maker and the series. If you paint landscapes and want a ready to use foliage green, a convenience mix is defensible. If you want to mix your greens from scratch and control their temperature, transparency and granulation, knowing the single-pigment options for blue green and yellow green becomes important.

The distinction that matters is use. A convenience colour used straight from the tube carries its multi-pigment composition onto the paper, but it does not mix those components with your other paints unless you mix it wet. A convenience colour used as a mixing base does.

The practical verdict

Single-pigment watercolours are not a guarantee of good results, and choosing them does not make mixing easier on its own. What they give you is predictability. When a mix fails, you can identify why. When a mix works, you can repeat it. That reliability becomes more valuable as your palette grows and your mixes become more complex.

Start by checking the codes on the paints you already use. You may find that most of your artist grade range is already single-pigment. The more useful discovery is usually which convenience colours have been carrying hidden pigments into mixes where you did not expect them.

What pigment codes actually mean: The code system is the foundation for understanding single-pigment paints. This article explains it in full.

Earth pigments and why they behave differently: earth pigments are some of the most important single-pigment colours.

Daniel Smith vs Winsor and Newton: both makers offer strong single-pigment ranges.