a public service announcement
This is actually wrong.
Firstly—CMYK is a color system. It’s used for an additive color system. They are not the only legitimate primary colors. They are the primary colors used in printing color systems. Color mixing is much more complex than that. For example, your computer screen (on which you are reading this lovely post) uses the RGB system, which means its primary colors are Red, Green, Blue.
Second, the color of ink and paint is determined by the pigment(s) used! If you are mixing paint, it’s best to make your choices based on the pigment contained in each paint, rather based on it’s color name. If you check the back of each paint tube, it will tell you the kinds of pigments used to create the color you see. All pigments have slightly different effects that you can come to understand, regardless of the medium (acrylic, watercolor, gouache, oil, even pastels). For example, Quinacridone pigments tend to be very transparent, and highly staining, while Cadmium pigments are more opaque. That’s why it’s always a good idea to buy paints that contain only one pigment, because if there’s only one pigment in each paint, then you can better predict what will happen when you mix the two pigments.
Lastly, since there aren’t any pigments that create a “true primary” all on their own, it’s best to use a tertiary palette to make primary and secondary colors (Yellow-Green, Yellow-Orange, Red-Orange, Red-Violet, Blue-Violet and Blue-Green) when mixing pigmented mediums. Using this system, you can make “true primaries” (like Red, using Red-Orange and Red-Violet) and you can make more subtle hues for whatever piece you happen to be working on. By using these six colors, you will have more precise control over the temperature and intensity of the colors you choose to create whatever effect you want.
Cadmium Red, Cadmium Yellow, Lemon Yellow (which is often the name of the paint, while the actual pigment is usually Hansa Yellow), Ultramarine Blue, Quinacridone Rose, and Phthalo Blue all happen to be the best pigments to use for a tertiary palette.
The important thing to remember is that these are pigments! While a paint may say “Magenta” it may not actually contain Quinacridone, and something that says “Lemon Yellow” may not contain Hansa Yellow. Hansa Yellow itself has the chemical name “arylide yellow” and may come in several different varieties.
Pigments listed on a paint tube are usually accompanied by their chemical name, such as “Arylide Yellow” and the Colour Index International name for the pigment, such as “PY 3”. You want only one “PY” number to be listed on a paint tube if you want a paint containing only one pigment.
Here are the main “tertiary pigments” (as I call them) and some of their properties:
Hansa Yellow = Yellow-Green
Hansa Yellows are sometimes called “Lemon Yellow,” but the important part is that their chemical name should be “Arylide Yellow,” (PY 3, PY 73, PY 97, etc). They should be bright, transparent and lightfast, with a coolish temperature.
Cadmium Yellow = Yellow-Orange
Cadmium Zinc-Sulfide (PY 35) is opaque and lightfast. It has a bright, distinctly warm temperature.
Cadmium Red = Red-Orange
Cadmium Seleno-Sulfide (PR 108) is opaque and lightfast. It’s bright and warm, and definitely a valuable pigment to include in any artist’s palette. Cadmium is bad for you, so take care not to have it around your food or anything. (But I tend to err on the side of paranoia.)
Quinacridone Rose = Red-Violet
Quinacridone Violet (PV 19). Quinacridone pigments in general tend to be high quality, expensive, transparent and staining. Go for the color name “Quinacridone Rose” rather than “Quinacridone Red” or “Quinacridone Violet”, because the later tend to be too purple or too red. The paints with the best pigments for a tertiary palette tend to be called “Quinacridone Rose.” The alternative to quinacridone rose is Alizarin Crimson, which isn’t as lightfast or as staining.
Ultramarine Blue = Blue-Violet
Polysulfide of Sodium-Alumino-Silicate (PB 29). It’s semi-transparent, even opaque-ish, and brilliant and it has a warm temperature, though sometimes it seems quite cool.
Phthalocyanine “Phthalo” Blue = Blue-Green
Copper Phthalocyanine (PB 15, PB 15:3 etc) is a powerful, dark, transparent and staining pigment. A little bit goes a long way, to such a degree that sometimes teachers won’t suggest it to a class of beginners. But it’s really not that scary.
And you don’t need to limit yourself to primaries or tertiaries either. There are other strong and useful pigments that can be used, including a palette of browns (Yellow Ochre, Raw Sienna, Burnt Sienna, Burnt Umbre & Raw Umbre), blacks, whites and even greens. Remember that even blacks and whites are not all the same. Ivory Black is more transparent than Lamp Black, and Titanium White is more opaque than Zinc White. Also, why waste all of your paint trying to mix up a perfect pinkish or yellowish flesh tone, when you could take the shortcut and use a bit of white and Naples Yellow?
There is this whole world of paint beyond the simple trick of mixing up a rainbow circle of colors with just a handful of colors. It’s super fun, but it’s not that important in the scheme of painting or art-making in general. So don’t listen to people who try to tell you that there is only way to do something in art! Paint is not that simple! Pigment is not that simple! Color is not that simple!
ART IS NOT THAT SIMPLE!