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 and maintained jointly by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists. Every commercially used pigment has an entry. The code you see on a tube is the Generic Name Code for that entry.
How to read it. The code follows a fixed format. P stands for pigment. The second letter names the colour family: B for blue, Y for yellow, R for red, 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.
The single-pigment rule, qualified. Single-pigment colours are generally the cleaner choice for mixing, because you know exactly what you are putting in. But that is not the same as saying they are always better. Some of the most useful convenience colours are deliberate mixtures, formulated because no single pigment hits the target.
What to buy
Jackson's Artist Watercolour, French Vermillion (PR242, 10ml)
A good example of a clearly labelled single-pigment warm red; the pigment code is shown on the listing and the tube.
Cass Art Artists' Watercolour, Indigo (PB15:1, PBK7, 10ml)
A useful illustration of a convenience mixture: two pigment codes on the label, honestly declared, producing a colour that works well in practice even without a single-pigment equivalent.
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.
Colour names are brand decisions. Pigment codes are not.
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 a combination of PR254 and PR170 or similar.
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
The most direct use of pigment codes is in palette building. If you know that PY43 is a transparent, moderately granulating warm yellow with excellent lightfastness, you can carry that knowledge across brands. If PY43 is discontinued in one range or reformulated, you know what you are looking to replace. If you want a neutral earth tone that will mix without going muddy, knowing that PBr7 covers a range of natural earth pigments gives you a starting point for comparison.
The codes also help when you are trying to avoid duplication. Two colours that appear different in the pan can carry the same code, which means they will mix in essentially the same way and occupy the same position in a palette. Buying both is usually unnecessary.
The system rewards a modest initial investment in learning the abbreviations. There are not many of them. Eight colour families, and the numbers take care of themselves once you are looking for them. 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.