10 Colour scales and legends

After position, the most commonly used aesthetics are those based on colour, and there are many ways to map values to colours in ggplot2. Before we look at the details, it’s useful to learn a little bit of colour theory. Colour theory is complex because the underlying biology of the eye and brain is complex, and this introduction will only touch on some of the more important issues. An excellent and more detailed exposition is available online at http://tinyurl.com/clrdtls.