On Tue, 12 Jan 2010, Ben wrote:

> Dear List,
> using the pgf build from 20100103 and texlive2009 from the Debian unstable
> I've just tried to do the following:
>
>    \enableregime[utf]
>    \usemodule[tikz]
>
>    \starttext
>
>    \startTEXpage
>    \pgfutil@definecolor{magenta}{rgb}{1,0,1}
>
>    \starttikzpicture
>      \draw (0,0) -- (1,1);
>    \stoptikzpicture
>    \stopTEXpage
>
>    \stoptext
>
> I always get
>
>    ! Undefined control sequence.
>    l.21 \pgfutil
>                 @definecolor{magenta}{rgb}{1,0,1}
>    ?
>    ! Emergency stop.
>    l.21 \pgfutil
>                 @definecolor{magenta}{rgb}{1,0,1}
>    End of file on the terminal!

You need to add \unprotect and \protect

\unprotect
\pgfutil@definecolor{...}
\protect

They are similar to \makeatletter and \makeatother in LaTeX.

The correct way is to ConTeXt's color mechanism to define colors. For 
example,

\usemodule[tikz]

\definecolor[mycolor][r=1,g=0,b=1]

\starttext
\starttikzpicture
   \node[text=mycolor] {Test} ;
\stoptikzpicture
\stoptext

This works with MkII but gives an error with MkIV.

! Undefined control sequence.
\pgfutil@registercolor ...ef \pgf@temp {\PDFcolor
                                                   {#1}}\edef \pgf@marshal 
{\...
\pgfutil@colorlet ...x \pgfutil@registercolor {#2}
                                                   \fi \edef \pgf@marshal 
{\n...
\tikz@next ...futil@colorlet {.}{\tikz@textcolor }
                                                   \fi \pgfsetcolor 
{.}\setbo...
l.7   \node[text=mycolor] {
                            Test}

That is because MkII and MkIV have a different color model, 
and tikz does not support the MkIV model yet.

I am attaching a fix for that. I do not know what is the best way to 
incorporate it into tikz (perhaps a pgfutils-mkiv.tex file). For the 
moment, you can just input it after loading tikz.

Aditya