There is a lot to know about color. Entire books have been written about it.

Various color systems exist and it is useful if you are familiar with them as a draftsman. Certainly as a professional draftsman / artist.

Daphne's method is based on the artist's color system. According to the color theory of the artist, there are three types of colors:

Primary colors, secondary colors and tertiary colors. The primary colors are red, yellow and blue Secondary colors are the result of a mixture of 2 primary colors; green, orange, purple.

Tertiary colors are the result of a mixture of 3 primary colors; brown. Shades are the result of a mixture of the above colors with black or white

Why is it important to know about this?

When mixing colors, it is of course useful to know what result the mixture of certain colors does. 

And you can not go without some knowledge of color if you want to enhance the composition of your drawing.

You can read more about this at level 3 use of color. click here