[Xy-pic] Default color model

[Vadim Radionov]

Hi Ross,

thank you for the explanation.

> Why do you need this?
>
> Once before I had to do this, since a publisher objected to having RGB in the PDF.
> Is yours a similar problem?

Yes, it's exactly my case.

> It was necessary to edit the PostScript dictionary file that is imported by dvips, changing a single specification of '0 0 0 setrgb' to '1 setgray'.
> Xy-pic has a command \dumpPSdict which gives a local copy of the PostScript dictionary, which you can then edit for the next run (with the \dump... command now commented). Consult the Xy-pic Reference Manual, for information about the PostScript drivers and back-end support.

I used your recipe with \dump and \usePSheaders.  There's no explicit
"0 0 0 setrgb" in the dump, so is it the line

/xycolor{0 1 2{xycolarray exch get}for setrgbcolor}def

that I have to change?  And is

/xycolor{0 setgray}def

a suitable replacement (it looks fine in my case, but probably I'm
breaking something)?

Thank you again,

Vadim