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.
At a glance
Single-pigment means one Colour Index code on the label. PB29 is one pigment. PB29 plus PV19 is two. The code tells you what is actually in the tube, which the colour name never does.
Single-pigment paints mix more cleanly. When two single-pigment colours meet on the paper, you have two pigments interacting. When two multi-pigment colours meet, you may have four or six. Each additional pigment increases the chance of a dull result.
Most artist grade ranges are mostly single-pigment. Winsor and Newton Professional and Daniel Smith Extra Fine label their pigments clearly. Check before you buy rather than assuming.
Some convenience colours are genuinely useful. A pre-mixed shadow colour or a convenience green is not a compromise if it saves time and you understand what is in it.
The pigment code is more reliable than the colour name. Burnt Sienna from two different brands may use entirely different pigments. The code tells you what you are actually buying.
What single-pigment actually means on the label
Every artist grade watercolour tube carries a Colour Index designation, a standardised alphanumeric code that identifies the specific pigment or pigments inside. PB29 is French Ultramarine. PY43 is Yellow Ochre. PR101 is a transparent iron oxide used in several Burnt Sienna and Transparent Red Oxide colours.
A single-pigment paint carries one code. A multi-pigment paint carries two or more, typically separated by a comma or listed in a series. “PB29, PV19” 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 all 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 PBr7 and another uses a synthetic iron oxide with a different code. The pigment code is the only consistent identifier.
For a full explanation of the code system, 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 are combining the characteristics of every pigment present.
A paint carrying two pigments, say a convenience orange made from PY83 and PR254, brings both of those pigments into any mix you make with it. Add a blue to that orange to darken it and you are now 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 neutral or subdued tone you were aiming for.
Single-pigment paints do not eliminate 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 even be aware of.
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, the mix is clean. If it looks grey or brown when it should not, one of the colours is a multi-pigment mix containing a pigment that is fighting the other one.
The pigment code is the only consistent identifier.
Which colours are worth buying in single-pigment form
Not every colour family has useful single-pigment options. Blues and earth colours are straightforward. Greens and oranges are harder to source in single-pigment form at reasonable prices. The most important palette positions to fill with single-pigment paints are those you mix from most often.
A core working palette built around single pigments might include:
A blue: French Ultramarine (PB29) is the standard choice. Transparent, granulating on some papers, and useful for mixing darks. Phthalo Blue Green Shade (PB15:3) is the colder, higher-staining alternative. Both are single pigment across all major brands.
A yellow: Hansa Yellow Medium (PY97) is one of the cleanest mixing yellows available. Transparent and warm without pulling towards orange too quickly. Daniel Smith is the most widely stocked brand carrying this specific pigment code in the UK, though it is not available in Winsor and Newton Professional. Winsor Yellow (PY154) is a useful alternative.
An earth colour: Burnt Sienna as PR101 is transparent and mixes cleanly with most blues to produce a wide range of useful neutrals. It is available from Winsor and Newton Professional and Daniel Smith Extra Fine, among others. The same pigment code appears under different colour names, so check the label rather than the name.
These three form the backbone of a limited palette capable of producing a wide range of colour through mixing. Whether you source them from a single brand or several, what matters is that each tube carries one code.
For UK stockists carrying these specific paints, this guide to watercolour suppliers in the UK covers the main options.
How to read a tube label and find the pigment code
On artist grade tubes, the pigment code or codes are almost always printed in small type on the side or back label. The designation follows a predictable format: a letter indicating the colour family (P for pigment, followed by B for blue, R for red, Y for yellow, G for green, Br for brown, and so on), then a number identifying the specific pigment within that family.
PB29 breaks down as: P (pigment) + B (blue) + 29 (the specific ultramarine formula in the Colour Index).
If there is more than one code, the paint contains more than one pigment. Some labels print these clearly separated by commas. Others list them one after another in a way that requires closer reading. If the label is hard to parse, the manufacturer’s product page will list the pigment composition, and the information is usually more reliable there than on third-party listings. Where pigment claims on retail sites differ from the manufacturer’s own page, the manufacturer’s page takes precedence.
Student grade paints sometimes carry this information and sometimes do not. This is one of several practical reasons to work with artist grade materials when budget allows, though the distinction matters most for paints you use in mixes rather than straight from the tube.
For further context on watercolour materials and how these choices compound across the rest of your practice, the materials section covers paper, brushes, and related decisions in the same level of detail.
Where multi-pigment convenience colours are still useful
The case for single-pigment paints is not a case against convenience colours as a category. There are multi-pigment mixes that behave well and serve specific purposes that single pigments cannot.
Payne’s Grey is a reliable example. No single pigment produces that particular cool, blue-leaning grey, and for painters who use it frequently, a well-made convenience mix saves time without producing unpredictable results in mixes, particularly if you use it 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 PG7 alone to three or four combined pigments depending on the brand and 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 into whatever it sits next to on the paper, but it does not mix those components with your other paints unless you actively mix it wet. A convenience colour used as a mixing base does.
What to buy: three single-pigment paints worth using
Verify pricing and availability at the time of purchase. Pigment compositions are occasionally revised, and the tube or the manufacturer’s product page is the definitive source.
Recommended paints
Winsor and Newton Professional
French Ultramarine (PB29)
The most useful starting blue for almost any palette.
Winsor and Newton Professional
Burnt Sienna (PR101)
A reliable two-colour neutral partner for PB29.
Daniel Smith
Hansa Yellow Medium (PY97)
A clean mixing yellow when PY97 matters.
Where to buy
The practical verdict
Single-pigment watercolours are not a guarantee of good results, and buying 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.