The Tertiary Colors

While secondary colors are mixed from two primaries, tertiary colors are mixed from all three primary colors. Tertiary colors encompass the vast array of brown hues. Overall, it is possible to mix approx. 100 000 differentiable hues; with the secondary colors you can mix "only" approx 160. Tertiary colors occur much more frequently in nature than secondary colors. The latter only decorate flowers, birds, fish and some reptiles and insects.
The following illustration shows three transparent foils, each in a primary color, i.e. red, green and blue; the upper foils have a higher transparency: green = 20% transparency, blue = 60% transparency, red = 60% transparency. In the middle, where the three foils are overlapping, we can see a tertiary color:

Tertiary color

This intersection in the middle is in no way a filling that has been produced by graphical work. Everybody can set up these foils with a graphic program: A good vector program has the option of assigning transparencies to an area. By entering the search word "transparencies" in the help menu of this program, you can find out if your own program supports this option.
Furthermore, you can obtain all brown hues by mixing the orange-red areas with black or gray:

Tertiary color

These modulations are very important for painters because you can mix any color you like when adding an appropriate quantity of black and/or white to a primary or secondary color.