By the end of this article you will be able to read any tube label, understand what the codes tell you and, just as usefully, what they do not.
Watercolour pigment codes are the most reliable piece of information on any paint tube, and most painters spend years ignoring them. That is not entirely their fault. The codes look like a chemistry shorthand designed to put people off, and the colour name is right there in large print, doing its best to reassure. The problem is that the colour name is, in many cases, nearly meaningless. The code is not nearly as impenetrable as it appears.
At a glance
What the code is. A pigment code is a standardised identifier from the Colour Index International, a reference system established in 1924 by the Society of Dyers and Colourists and jointly maintained since the mid twentieth century with the American Association of Textile Chemists and Colorists. The code you see on a tube is the Colour Index Generic Name for that entry.
How to read it. The code follows a fixed format. P stands for pigment. The letter or letters following it name the colour family: B for blue, Y for yellow, R for red, O for orange, G for green, V for violet, Br for brown, Bk for black. The number identifies the specific pigment within that family. PB29 is Pigment Blue 29, known as Ultramarine Blue. PY43 is Pigment Yellow 43, natural Yellow Iron Oxide. PR101 is Pigment Red 101, synthetic Red Iron Oxide.
What it tells you. Which pigment is in the paint. Whether the colour is a single pigment or a mixture. Whether the pigment is the same across two tubes from different brands, even if the colour names are entirely different.
What it does not tell you. How the paint will behave. Concentration, grind, binder, and formulation all affect transparency, granulation, staining, and handling. Two tubes sharing a pigment code can look and behave quite differently.
A label in practice. A warm red labelled with one code, such as PR242, tells you that one pigment is doing the work. A colour labelled with two codes, such as PB15:1 and PBK7, tells you it is a manufactured mixture. The ratio remains the manufacturer’s choice.
The system behind the codes
The Colour Index International assigns each pigment two identifiers: a Constitution Number, which describes its chemical structure, and a Generic Name Code, which is the one artists work with. The Generic Name Code is what appears on tubes: PB29, PY43, PR101. It is consistent across manufacturers and markets. If a French manufacturer and a British one both use PB29, they are using the same pigment, even if one calls it Ultramarine and the other calls it French Ultramarine Deep.
That consistency is the point. Colour names are brand decisions. Pigment codes are not.
PBr7 is worth knowing specifically because it covers a family of natural earth pigments. Raw Sienna, Raw Umber, Burnt Umber, and several others can all carry that code, because they all derive from the same natural iron oxide class. The code tells you the pigment family; the colour name tells you roughly where in that family the manufacturer has positioned the mix. Neither is complete without the other.
The number within a code is chronological. PB29 was the twenty-ninth blue pigment entered in the index. A lower number does not mean older chemistry, simpler composition, or worse quality. A higher number does not mean the opposite. The numbering is purely administrative, and treating it as a quality ranking is one of the more persistent misreadings of the system.
Why colour names are not enough
The clearest way to see why pigment codes matter is to look at what happens without them. Burnt Sienna is a good case. It is one of the most widely used earth colours in watercolour, and the name suggests a specific, stable identity. In practice, Burnt Sienna from one brand may use PBr7, a genuine natural earth; from another it may use PR101, synthetic Red Iron Oxide, or a mixture of both. The handling and mixing behaviour of those pigments differ. A natural PBr7 Burnt Sienna tends to granulate more and mix in a particular way. A synthetic version may be more uniform, more opaque, stronger in tint.
Neither is wrong. But if you are choosing between them, or trying to substitute one for another, the colour name gives you almost nothing. The pigment code gives you the information you actually need.
This matters most when you are building a palette, sourcing a pigment from a different brand, or trying to understand why a colour behaves unexpectedly. Manufacturers occasionally reformulate; when they do, the pigment code changes before the colour name does. The code is where a reformulation first becomes visible.
A full reference for currently registered pigments, including Colour Index numbers, is maintained by the Colour Index International, and is the most reliable source for checking codes against pigment identity.
What the codes cannot tell you
Knowing the pigment code is not the same as knowing how a paint will perform. Two tubes carrying PB29, Ultramarine Blue, can have meaningfully different transparency, granulation, and tinting strength depending on how the pigment has been processed and what it has been combined with. The binder, the grind, the ratio of pigment to vehicle: all of these affect the paint on paper. The pigment code identifies the raw material. It does not describe the final product.
This is where reviewing and testing genuinely matters, and where articles about lightfastness in watercolour paints become relevant, because lightfastness is another property that pigment identity suggests but does not fully determine. A pigment with a strong lightfastness record can still perform inconsistently depending on formulation and concentration.
The same caution applies to mixed pigment paints. The Cass Art Indigo listed above carries two codes: PB15:1 (Phthalo Blue, green shade) and PBK7 (Carbon Black). Knowing that tells you it is a manufactured convenience colour rather than a match for the historic natural indigo dye, and it tells you something about how it will behave in a mixture. Phthalo Blue is strong and can dominate. It does not tell you the ratio of the two pigments, which the manufacturer is not obliged to disclose.
Reading a label in practice
The tube tells you more than most painters realise. The pigment code or codes appear somewhere on the body of the tube, often near the colour name or on the back panel. On professional ranges they are almost always present; on student ranges they are sometimes absent or listed as “Hue,” which signals a pigment substitute rather than the original.
A colour listed as Cadmium Red Hue, for instance, is not cadmium. It is a mixture formulated to approximate cadmium’s appearance without the cost or the handling restrictions that cadmium pigments carry. That is a perfectly legitimate product, but it is a different product, and the code will confirm it. Genuine cadmium red carries PR108; the hue version will carry something else, often built from pyrrole or naphthol reds such as PR254 or PR170, though the exact substitution varies by brand.
Some proprietary ranges, and some convenience colours sold in certain markets, do not disclose full pigment data on the product page, even when it appears on the tube. The advice is consistent and simple: check the tube label directly, not the product listing. Product pages are written for search engines as much as for painters. The label has to comply with labelling requirements and is the more reliable source.
Jackson’s maintains detailed pigment information on their product listings, which makes cross-referencing easier than with some other retailers. A small but useful thing when you are building a palette around specific pigments rather than colour names.
A practical approach
Use the code when you need to identify a paint across brands, check whether a familiar colour name has been reformulated, or understand whether a tube contains one pigment or a mixture. The system rewards a modest initial investment in learning the abbreviations. After a short while, reading a tube label becomes fluent, and the colour name retreats to what it always was: a shorthand for marketing, not for paint.
For the next question — how to choose single-pigment colours for a working palette — use the guide to single pigment watercolours.
What to read next
Lightfastness in watercolour: what the ratings mean and which pigments to avoid.
The ASTM lightfastness scale and the Blue Wool scale are both used on tube labels. This article explains what each rating means, which pigments have a poor record, and why fugitive colours can still be worth using in specific contexts.
Building a limited palette: how to choose pigments rather than colours.
A six-colour palette built around pigment codes rather than colour names will mix more cleanly and last longer than one assembled by colour name alone. This article works through the logic from first principles.
Winsor and Newton Professional vs Daniel Smith, tested across twelve pigments.
Both ranges publish full pigment data. This comparison tests the same pigment codes across both manufacturers for colour, transparency, granulation, and tinting strength.
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