The Secret of Single Pigment Colors

I recommend that painters use only single pigment colors. That is, colors that are made using only one pigment. I suggest this for the same reason that I advise painters to keep color mixing to a minimum. The more colors that are mixed together, the duller and more muddy looking the result. In my university painting courses I was taught to use only the 3 primary colors and to mix all of my hues from there. This is in contrast to the great painters of the past who, for hundreds of years, only mixed colors for specific effects, otherwise they applied pure, single pigment colors and any mixtures were done in transparent or translucent layers, or opaque wet in wet (Ala Prima), essentially keeping them 'separate' to preserve the luminosity and color intensity. Consider too, that for many centuries, until the Industrial Revolution, artists were limited to a palette of not a lot more than a dozen colors. Even the Impressionists had fewer than 1/3 of the variety we have today.

Most paint manufacturers produce color charts for the range of colors that they offer. You can look at these on their websites or in the art supply stores. Manufacturers typically offer a selection of colors of which around 25% or more are mixtures of two or more pigments. A quick glance at a color chart of a well known manufacturer of acrylic paints shows 85 colors of which around 70 are single pigment. If you go to any manufacturer’s site, check the color charts at art stores, or just read the tubes, you will be able to discern for yourself which ones are composed of more than one pigment. Perhaps the quickest reference technique is to look for the ‘color index’ right on the tube, that is the letter/number assigned to each color, for example, PY35 is Cadmium Yellow Medium. If a color has more than one color index, it is not a single pigment color. A color named Cadmium Red Hue it is not a single pigment color and will have more than one index assigned to it: PR5 (Napthol Red) and PR207 (Quinacridone Red) for example.

Also, beware of colors that are not named after the pigment used to create them. Hooker’s Green, Payne’s Grey, and so on. Why let paint manufacturers mix colors for you? I only use single pigment colors. You can make the color yourself by mixing those pigments together, or as I would prefer to do, layer them in transparent glazes and/or veils to create a comparable color effect that is much more vibrant and 'painterly'. By making your own version of the color you will also have more creative control over the look of the color simply by adjusting the amounts of each color or in the way they are applied. Check out these examples of popular mixed colors offered by many manufacturer’s compared with a combination of the same pigments used to make the equivalent hue, only applied in transparent layers (glazes):

 Let’s take a look at a popular green hue that many artists, esp landscape painters like to use: 
The reference code, or color index, for phthalo Green is PG 36, only one pigment in the mix. SAP GREEN ref code is PR101, PY150, PG36, PBK. That is 4 pigments: trans red oxide, nickel azo yellow, phthalo GREEN, and carbon black.

It's a nice natural looking GREEN hue but the point here is that you can use those 4 colors in dozens of different combinations, using different techniques like impasto and transparent effects to make your own dynamic, sumptuous, vibrant, and more 'painterly' versions of SAP GREEN that will have the new admirers of your art dazzled by your subtle and clever creative brilliance.

Here are some examples of the manufacturer's mixed, multiple pigment colors, the ones on the left, beside versions created by simply applying those same individual pigments in transparent layers (glazes).  The bottom one is the SAP GREEN discussed above.  The paint sample on the far left is the SAP GREEN you can buy from the manufacturer.  The other 4 are different variations created by using those 4 pigments in alternating transparent glazes.