Changing the color palette

In order to reduce the number of styles used, I use the CellUtil class.
However it only works if the colors are indexed colors. See:

https://bz.apache.org/bugzilla/show_bug.cgi?id=59442

So, I now only use indexed colors. But I'm not really pleased with the
default colors and would like to change them. I know this was possible
using the getCustomPalette() method of the HSSFWorkbook class. But how can
I do this using the XSSF user model? Or is it possible to use both HSSF and
XSSF?

/Bengt