The colours for bar chart series are not very appealing when more than two series are being plotted. The colours used for pie chart data points are generated using a routine that I have written, but it is not very elegant.
I would like to make use of a pre-written library, and think that chroma.js (http://github.com/gka/chroma.js) will work well. It will enable the use of colour scales similar to those on the ColorBrewer site (http://colorbrewer2.org/): http://github.com/gka/chroma.js/wiki/Predefined-Colors.
I have already implemented this library when working on issue
#332, but thought that it was worth having it as a separate issue.