[XeTeX] \font "<platform font>":color=FFFFFF produces black, not white glyphs

[Khaled Hosny]

On Sun, Mar 29, 2015 at 02:54:49PM +0100, Philip Taylor wrote:
> Could anyone explain why the continuum that exists from color=000000 to
> color=FEFFFF, color=FFFEFF and color=FFFFFE breaks at color=FFFFFF ?
> 
> To ensure 100% consistency between the proofing version of a book (which has
> marginal notes in red to ensure that the proof-reader can unambiguously
> identify the callouts for each image) and the CRC-ready version, I prefer
> not to disable the marginal note mechanism, which /might/ lead to different
> pagination (although tests suggest, but cannot prove, that it does not) but
> instead to make the marginal notes invisible by changing their colour from
> DF0000 to FFFFFF.
> 
> However, when I do so, the glyphs that should be white are, in fact, black.
> I can fudge my way around this by using (e.g.,) the colour specifier FFFFFE,
> but I have a pathological dislike of kludges and would like to know why
> 
> 	\font "<platform font>":color=FFFFFF
> 
> produces black, not white glyphs.

That is a bug in xdvipdfmx; FFFFFF will be converted by XeTeX to
FFFFFFFF when written to the XDV, but xdvipdfmx uses the 0xFFFFFFFF
value to mean that no color have been selected so ends up ignoring the
color here. A work around is to set the color to FFFFFF00 (or any other
value for the alpha since xdvipdfmx does not support transparency
currently).

Regards,
Khaled