That's because this pure pigment leans away from Orange and mixes harmoniously with the cool pure Blue. In this example, if you want to mix a rich Purple instead, use a cool pure Red such as Quinacridone Red. This result is only great if you actually want a rich Brown. The three primary colours shown are red, yellow, and blue. In this case it's pure Blue + pure Orangey/Red. It also helps you to introduce and explain colour theory as it boldly displays the relationships between primary, secondary, and tertiary colours. Colour wheels, much like this interactive colour wheel, can be used to: show the relationship between different colours.

Brown is the neutralized result we get from mixing Complementary colors. Colour wheels normally appear as circular charts that show primary colours in relation to secondary and tertiary colours. In our example above, Cadmium Red is a warm pure hue, leaning toward Orange. Blue and Orange are Complementary Colors. Traditionally, it contains 12 hues 3 primary colors, 3 secondary colors, and 6 tertiary colors. As a result, there are many different pure Yellow, Red and Blue pigment paints available. Paint is manufactured with organic, mineral and chemical pigments. They are unmixed pigments that can't be created by mixing other colors. To understand why, we need to look at paint pigments. A Primary Yellow, Red or Blue paint color usually refers to a paint that contains only one pigment. For instance, if you mix Cadmium Red + Ultramarine Blue, you'll likely be sadly disappointed. If you were expecting a deep rich Violet (Purple), the resulting Brown will be a total surprise. The problem is paint pigment never works like that in real life. However, as I wrote in a previous Color Wheel post, color is not an exact science. So in other words, you could conceivably mix gazillions of colors with only three pure Primar y pigments of Yellow, Red and Blue. Of course that's what they teach us in school.

Color wheels primary and secondary