[pgf-tikz] RGB colour model for plain TeX users

[Taylor, P]

Jim Diamond wrote:
> [A] couple of minutes of playing
> around gave me
>
> \def\pgfutil at emu@cmyk#1#2,#3,#4,#5\@nil
> {
>      \pgfmathsetmacro{\@red@}{(1 - #2) * (1 - #5)}%
>      \pgfmathsetmacro{\@green@}{(1 - #3) * (1 - #5)}%
>      \pgfmathsetmacro{\@blue@}{(1 - #4) * (1 - #5)}%
>      \expandafter\edef\csname\string\color@#1\endcsname
>      {\noexpand\xcolor@ {}{}{rgb}{\@red@,\@green@,\@blue@}}
> }
>
> I realize that converting cmyk to rgb is a lot more contentious than
> converting RGB to rgb,

I think that it is more than "contentious"; I think that it is genuinely 
dangerous.  I don't know whether PGF supports CMYK — if it does, then 
wonderful.  But if it does not, and if the addition of \pgfutil at emu@cmyk 
were to suggest that it does, then that could lead users to believe that 
they are generating CMYK graphics when they are in fact generating RGB.

Philip Taylor