We've been having a similar issue for a while now - but it turned out to be something relatively simple. In our case, if you specify a colour for the dataset and include a leading '#' character, the bars are rendered with the correct colour but every series in the legend was represented with the same grey box. Mucho frustrating,..
This is not exactly the same as the font problem described by other posters above, but I've posted a reply here incase it saves someone an hour or two of messing around if they find themselves in this thread.
Bad Kitty:
<dataset seriesName="Series ABC" color="#CC0000">
Good Kitty:
<dataset seriesName="Series ABC" color="CC0000">
Simple...
