Is there a way to iterate over all defined colors without mentioning them again?

Question

Situation

Let's say I have defined some colors. I'd like to produce a test page that functions as a color-key for developers.

Example

The defined colors colora, colorb, and colorc should be iterated without mentioning them explicitly again (happens automatically). This is efficient programming in that I can have an arbitrary number of colors (perhaps 50 or so) and create a time-saving color key.

\documentclass{article}
\usepackage{fontspec}
\usepackage{tikz}
\usepackage{pgffor}

\definecolor{colora}{cmyk}{0,.5,1,.3}
\definecolor{colorb}{cmyk}{.4,.6,.5,.1}
\definecolor{colorc}{cmyk}{.6,.2,.5,.2}

\begin{document}

%\foreach \definedcolor in {defined colors} % pseudo-code
%   \tikz \node [fill=definedcolor, minimum width=2cm, minimum height=1cm,text=white] {name of defined color}; % pseudo-code
\color{colora} COLORA

\color{colorb} COLORB

\color{colorc} COLORC
\end{document}

Answer 1

One possible way is to intercept the color definition with your own macro.

\documentclass{article}
\usepackage{tikz}


\def\appendcolor#1#2#3{%
\csname pgfutil@ifundefined\endcsname{definedcolorsofar}{\def\definedcolorsofar{#1}}{%
\expandafter\def\expandafter\definedcolorsofar\expandafter{\definedcolorsofar,#1}}%
\definecolor{#1}{#2}{#3}%
}

\appendcolor{colora}{cmyk}{0,.5,1,.3}
\appendcolor{colorb}{cmyk}{.4,.6,.5,.1}
\appendcolor{colorc}{rgb}{1,0,0}
\appendcolor{colord}{rgb}{0,0,1}

\begin{document}
\tikz{
\foreach \x[count=\xi] in \definedcolorsofar 
   \node at (0,\xi)[fill=\x, minimum width=2cm, 
           minimum height=1cm,text=white] {\x}; 
}

\end{document}