It’s useful, in understanding how to mix color, to start off with a limited palette and gradually increase the number of colors. Better that than buying every color “off the shelf,” a very expensive proposition.
The primary color wheel is composed of red, yellow and blue. The question is, which red, yellow and blue. Whether you are just starting out as a painter or whether you’ve been painting for years, I recommend you start out by making a color wheel using only three colors. The paint supply company Daniel Smith has a set of colors they feel represent the “primary hues,” consisting of Cadmium Yellow Light Hue, Pyrrol Scarlet , Permanent Blue and Titanium White. I have not checked this out yet. They also have Primary Cyan, Primary Magenta and Primary Yellow in their Golden Heavy-bodied acrylics. You might try these, or simply restrict yourself to a red, yellow and blue from your basic kit for this exercise. (I would recommend cadmium yellow, cadmium red and ultramarine blue.)
Draw a double circle and divide it into 6 segments like a pie. I suggest that you use only Cadmium (or Hansa) Yellow Medium, Cadmium Red, and Ultramarine Blue. Make a triangle between three of the portions. Fill one slice with yellow, one with red, and one with blue. These are the “primary colors.” Save this exercise. We’ll add to it after I explain a couple more concepts.
There’s no absolute agreement on which three colors are the “real” primary colors, just that they are red, yellow and blue. It was believed that from these three colors, you could product any other color.
To test that, mix your red with yellow to produce an orange and put that color between the red and yellow. Then do the same with red and blue and with blue and yellow. Theoretically, this produces the secondary colors: orange, green and purple. But you will notice that the colors produced are not of the brightest (most saturated) hue. I’m going to assert that that is because the color temperature of the three colors used is not correct. (I’ll cover that more in the section on temperature.)
Here's an example of a "limited-color" color wheel. I did this one with yellow, alizarin crimson and ultramarine blue.
Complements: Each pair of primary plus secondary color is referred to as “complementary.” So red and green are complementary, blue and orange are complementary, and yellow and purple are complementary. Complementary colors, when mixed in paint, result in black. You’ll find that red and green make an excellent black (particularly alizarin crimson and thalo green). Ultramarine Blue and Burnt Sienna (which is actually a dulled down orange) make a very satisfactory black. I’ve never yet gotten a satisfactory black from the yellow-purple combination but probably I’ve just not found the exact complements.
Analogous colors: While complementary colors are across from each other on the color wheel, analogous colors are next to each other. For instance, yellow and red can be viewed as analogous to orange.
Color harmony: This has a lot to do with color harmonies. If you want a very bold (and sometimes unpleasant) contrast, use complementary colors -- particularly if you can get them to the same value. (See discussion of value to follow.) If you want a very harmonious (and possibly a bit dull) picture, work only with a range of analogous colors.
(There could be an exercise here.)
In learning color, it’s useful to start with a limited palette. Working only with the original limited palette, you can produce a wide range of colors. So bear with me while we work some more on the color wheel exercise.
Define a circular area at the center of the color wheel that you made. Mix red, yellow and blue until you get a color close in tone to pure black. Add that black to the center of the color wheel. Notice that across from each primary color is a secondary color. If you mix any of the complementary pairs in the proper proportions, you should get black. However, if you mix in incorrect proportions, you will get the neutral colors (browns and grays.)
You’ve defined, in the exercise above, the Primary (red, yellow, blue) and secondary (orange, purple, green) colors around the theoretical color wheel. This is not a perfect system, but it’s useful to know for color mixing. You could define tertiary colors by painting those colors that fall between each color you have put on the chart. I would, at this point, simply buy a color wheel but it’s a good exercise if you are just familiarizing yourself with the color-mixing process and need practice.
Now, if you recognize that a 3-color-plus-white limited palette will not give you all the secondary colors, what will? Well, you could simply buy 6 colors: Yellow, orange, red, magenta, blue, and green. That would do it. A possible 9 color palette would include Cadmium Red, Alizarin Crimson, Cadmium Orange, Cadmium Yellow, Viridian, Ultramarine Blue, Phthalo Blue, Dioxazine Purple and a large Titanium White. Or you could buy a warm and cool version of each primary color. We’ll do a warm-cool color wheel in the temperature section.
There’s another exercise that will improve your familiarity with the mixing of complements. On a page, put a smear or square of yellow, red, and blue on the left side. Then put a smear or square of purple, green and orange (each opposite its complement) on the right side. Draw the complements towards each other in the middle, keeping a clean brush. When you reach the center, you should have a medium gray. As you move back towards the left and right sides, try to capture the gradients of brown neutrals (on the one hand) and gray neutrals (on the other.) This exercise requires that you keep your brush very clean or work with multiple brushes.