[XeTeX] Background color does not work

[Carlos R. Mafra]

I am trying to modify the background color of a book I am typesetting using
'xetex'.

After searching on google I found the command

\special{x:backgroundcolor=color}

being mentioned on "About XeTeX" by Jonathan Kew. In that file it is
mentioned that 

"The transforms.tex sample file demonstrates use of most of these \specials."

so I downloaded that file from the XeTeX homepage (it is inside XeTeX_doc.zip)
and tried to compile it with 'xetex'.

The \special above does not work and I get this warnings (among others):

[mafra at Pilar:Samples]$ xetex transforms.tex
This is XeTeX, Version 3.1415926-2.2-0.9997.4 (TeX Live 2010)
 restricted \write18 enabled.
entering extended mode
(./transforms.tex [1]
** WARNING ** No valid color specified?
** WARNING ** No valid color specified?
** WARNING ** Interpreting special command backgroundcolor (x:) failed.
** WARNING ** >> at page="1" position="(72, 769.89)" (in PDF)
** WARNING ** >> xxx "x:backgroundcolor=FFFFDD"
** WARNING ** >> Reading special command stopped around >>=FFFFDD<<

The pdf is produced but the background color does not have any effect (I tried
some different colors too).

Does anyone have an idea about what is going wrong here and how to fix it?