This may be of no use to you at all as it's not for charts generated directly with XML, but if you use FusionCharts with PHP you can use php class. Then you can set your own color palette in the file fusioncharts_gen.php. Just search the file for the string
function colorInit()
and put your own hex codes in place of the defaults.
Read the documentation "Use with PHP" first and then go through "FushionCharts with PHP Class" and finally do the examples in "Using with PHP Class" This sounds daunting but it's really not that difficult and might be the best answer for you.
Good luck!
--Liz
