How to use CMYK-Colors in the whole document

Question

I found out, that my color laser printer prints graphics with gray color in RGB-Representation instead of using black (they are more red then gray). So it seems, that PDFLaTeX is creating RGB-PDF-Files.

I only use pstricks-graphics like this one:

\documentclass[letterpaper,dvips]{article}

\usepackage[utf8]{inputenc}
\usepackage{textcomp}

\usepackage{pst-all}

\usepackage{color}

\begin{document}

    \pagestyle{empty}
    \begin{TeXtoEPS}
        \psset{xunit=1cm,yunit=1cm,runit=1cm}
        \begin{pspicture}(2,2)
            \psset{linewidth=1pt}

            \psframe[fillstyle=solid, linewidth=1pt, fillcolor=lightgray](2,2)

        \end{pspicture}

    \end{TeXtoEPS}

\end{document}

I'm creating eps-files with this steps:

• latex Grafik1.tex
• dvips Grafik1.dvi -o Grafik1.ps
• ps2eps --ignoreBB Grafik1.ps

and include the eps-file with \includegraphics

So is there a way to tell the whole document only create CMYK-Colors or an other way to create a document with the wright colors?

EDIT: The basic Problem is solved, but when creating a gradient, colors are used instead of black

\documentclass[letterpaper,dvips]{article}

\usepackage[utf8]{inputenc}
\usepackage{textcomp}

\PassOptionsToPackage{cmyk}{xcolor}% NB: put this *before* \usepackage{pst-all}
\usepackage{pst-all}


\begin{document}

    \pagestyle{empty}
    \begin{TeXtoEPS}
        \psset{xunit=1cm,yunit=1cm,runit=1cm}
        \begin{pspicture}(2,2)
            \psset{linewidth=1pt}

            \psframe[fillstyle=gradient, gradbegin=white, gradend=black](2,2)

        \end{pspicture}

    \end{TeXtoEPS}

\end{document}

Answer 1

Drop the \usepackage{color} and load pstricks this way (because pstricks loads xcolor for you already, at the proper moment):

\PassOptionsToPackage{cmyk}{xcolor}
\usepackage{pst-all}