`\definecolor` within `\foreach` loop

Question

I am trying to make this loop work:

\foreach \name/\col in {first/{204, 0, 0},%
                       second/{0, 102, 0},%
                        third/{0, 0, 153}}{%
    \definecolor{\name}{RGB}{\col} % buggish line
    \expandafter\xdef\csname\name\endcsname##1{\noexpand\textcolor{\name}{##1}}
    % + more convenience utilities..
}

.. but the colors seems not to be defined, since I get

! Package xcolor Error: Undefined color `first'.

When I try to use them. I have try to fiddle-faddle with many combinations of \expandafter, \noexpand, \relax etc. with no success and no real strategy. What is the reasoning to get them right?

In the end, I expect:

here is a \first{custom}-\second{colored} \third{text}

to produce:

Answer 1

For the same reason you need \xdef, you need \xglobal\definecolor (section 2.5.5 in the manual of xcolor).

\documentclass{article}
\usepackage{xcolor,pgffor}

\foreach \name/\col in {%
  first/{204, 0, 0},%
  second/{0, 102, 0},%
  third/{0, 0, 153}%
}{%
  \xglobal\definecolor{\name}{RGB}{\col} % buggish line
  \expandafter\xdef\csname\name\endcsname##1{\noexpand\textcolor{\name}{##1}}
  % + more convenience utilities..
}

\begin{document}

here is a \first{custom}-\second{colored} \third{text}

\end{document}

I'd be wary about using such an approach, because you risk to overwrite commands, with possibly disastrous effects.

Here's code that's free of that problem (colors are silently overridden, though):

\documentclass{article}
\usepackage{xcolor,xparse}

\ExplSyntaxOn
\NewDocumentCommand{\definebunchofcolors}{m}
 {
  \clist_map_inline:nn { #1 }
   {
    \iagolito_define_color:n { ##1 }
   }
 }
\cs_new_protected:Nn \iagolito_define_color:n
 {
  \__iagolito_define_color_aux:nn #1
 }
\cs_new_protected:Nn \__iagolito_define_color_aux:nn
 {
  \definecolor{#1}{RGB}{#2}
  \cs_new:cpn { #1 } ##1 { \textcolor{#1}{##1} }
 }
\ExplSyntaxOff

\definebunchofcolors{
  {first}{204, 0, 0},
  {second}{0, 102, 0},
  {third}{0, 0, 153}
}

\begin{document}

here is a \first{custom}-\second{colored} \third{text}

\end{document}

However, you don't gain much with this approach: it's simpler to do one declaration at a time.

\documentclass{article}
\usepackage{xcolor,xparse}

\ExplSyntaxOn
\NewDocumentCommand{\setupcolor}{mO{RGB}m}
 {
  \definecolor{#1}{#2}{#3}
  \cs_new:cpn { #1 } ##1 { \textcolor{#1}{##1} }
 }
\ExplSyntaxOff

\setupcolor{first}{204, 0, 0}
\setupcolor{second}{0, 102, 0}
\setupcolor{third}[rgb]{0, 0, 0.6}

\begin{document}

here is a \first{custom}-\second{colored} \third{text}

\end{document}

Answer 2

Definitions in a \foreach loop are local (unless made global), so the definitions of the colors with \definecolor are unknown outside, in particular when you try to access them with your \textcolor command.

Why do you use a loop? I see no advantage of \foreach \x in {a,b,c} {\dosomething{\x}} over \dosomething{a}\dosomething{b}\dosomething{c}.

\documentclass{article}
\usepackage{xcolor}
\newcommand\newcolor[2]%
  {\definecolor{#1}{RGB}{#2}%
   \expandafter\newcommand\csname#1\endcsname[1]{\textcolor{#1}{##1}}%
   % + more convenience utilities..
  }
\newcolor{first}{204, 0, 0}
\newcolor{second}{0, 102, 0}
\newcolor{third}{0, 0, 153}
\begin{document}
here is a \first{custom}-\second{colored} \third{text}
\end{document}