A frequently asked question is, 'how does one customise the colours in a chart?'  Below is a link to a blog post from Brian Welcker, which is actually a post on how to overcome the encumberence of the chart legend when it takes up too much space on a chart.  The example takes advantage of some code stored directly in the report; you can see it by choosing Report - Report Properties and then the code tab.  As a bonus you can see some cuning use of a .NET hash table to share colours consistently between a chart and a surrogate legend.

http://blogs.msdn.com/bwelcker/archive/2005/05/20/420349.aspx