[XeTeX] Grey fonts with XeTeX

[Philip Taylor]

Although I normally work with full-colour projects, the financial constraints of a current project require me to avoid colour on any page on which it is not strictly necessary (that is, to avoid colour on any page that does not carry a coloured image or on which coloured text is essential).  I found by a process of experiment that I can achieve grey rules using a combination of "eplain" and the "color" package, as in (e.g.,) :  \headlinerule = {\color [gray] {0.85}\hrule height 0,95 pt depth 0,95 pt} but what if I want a grey font ?  The XeTeX documentation makes no mention of CMYK at all, and whilst I can achieve the /effect/ of gray by using a suitable admixture of RGB, the resulting text is reported by Adobe Acrobat pre-flight checks as "not black".  Is there any way of achieving /real/ grey text so that all non-coloured pages are black-only ?  I have tried playing with the "transparency" hex pair that can optionally follow the RGB specifier, but it appears to offer either
full transparency or none at all, with no intermediate possibilities.

Philip Taylor