[XeTeX] Colour specials for XeTeX

[Akira Kakuto]

Dear Philip,

xdv2pdf was a driver for MacOS by Jonathan.
If you use -no-pdf option and apply xdvipdfmx to a created
.xdv file, you can see messages like

xdvipdfmx:warning: xetex-style \special{x:rulecolorpush} is
not supported by this driver;

I don't know details, perhaps \special{x:something}
may not be supported in xdvipdfmx except for a few ones.

Best,
Akira