Tikz nodes - command for its color

Question

Is there a command that lets me use the color of a certain node (e.g. the node with the name "Node 1")? Something like \nodecolor{Node 1} or similar? I am trying to use the color of a certain node as a variable.

Answer 1

Here's at least a proof of concept for the text color for TikZ and LaTeX (since then xcolor is used which allows to \xglobal a \colorlet).

This lets a color named pgf@sh@c@<node name> to the color that is either currently active (.) and would be used for the text as well or the one that is defined via text = <color>.

The \nodecolor macro silently reverts to the current color when the color for the given node name doesn't exist.

---

Similar things can be done to \tikz@strokecolor and \tikz@fillcolor, though I wonder if the node's text box is really the right place to hook this in but it is the first easy one I found.

There's also more do be done for nodes of the same name but in different pictures.

---

It would be very easy to also save the color name, e.g. . or blue in this case, but this is not really a good idea since these names can be overwritten or are very dynamic (in the case of .).

Code

\documentclass{article}
\usepackage{tikz}
\makeatletter
\newcommand*\nodecolor[1]{\@ifundefinedcolor{pgf@sh@c@#1}{.}{pgf@sh@c@#1}}
\tikzset{
  save text color/.style={
    execute at begin node=% latex only
      \ifx\tikz@textcolor\@empty
        \xglobal\colorlet{pgf@sh@c@\tikz@fig@name}{.}%
      \else
        \xglobal\colorlet{pgf@sh@c@\tikz@fig@name}{\tikz@textcolor}%
      \fi}}
\tikzset{anchor=base,baseline=0pt}
\begin{document}
\tikz[green]\node[ultra thick, draw=blue, fill=red, save text color] (Node 1) {Node 1};
The color of \textcolor{\nodecolor{Node 1}}{Node 1}.
\tikz       \node[ultra thick, draw=blue, fill=red, text=yellow, save text color] (Node 2) {Node 2};
The color of \textcolor{\nodecolor{Node 2}}{Node 2}.
\tikz\shade[left color=\nodecolor{Node 1}, right color=\nodecolor{Node 2}] circle[radius=2ex];
\end{document}

Output

Answer 2

As announced above, here is a slightly modified and expanded version of Qrrbrbirlbel's code. This version uses user-readable colour names (without @) that can be used directly again in TikZ options.

I have also extended the principle to stroke, fill and concept colours (of mindmaps), which are all stored in similar variables in the PGF/TikZ innards.

If this question/answer makes it into tikz-ext, feel free to use this code.

% !TEX TS-program = pdflatex
\documentclass[tikz]{standalone}
\usetikzlibrary{mindmap}
\colorlet{root-color}{blue}
\colorlet{root-textcolor}{red}
\colorlet{col1}{red}
\colorlet{col2}{green}
% 
%%% Saving node colors
%%% see <https://tex.stackexchange.com/questions/660876/tikz-nodes-command-for-its-color/662011#662011> 
% 
\makeatletter
\newcommand\nodetextcolor[1]{@ifundefinedcolor{text color of #1}{.}{text color of #1}}
\newcommand\nodefillcolor[1]{@ifundefinedcolor{fill color of #1}{.}{fill color of #1}}
\newcommand\nodedrawcolor[1]{@ifundefinedcolor{draw color of #1}{.}{draw color of #1}}
\newcommand\nodeconceptcolor[1]{@ifundefinedcolor{concept color of #1}{.}{concept color of #1}}
\tikzset{
  save node text color/.style={
    execute at begin node=% latex only
      \ifx\tikz@textcolor@empty
        \xglobal\colorlet{text color of \tikz@fig@name}{.}%
      \else
        \xglobal\colorlet{text color of \tikz@fig@name}{\tikz@textcolor}%
      \fi
    },
  save node draw color/.style={
    execute at begin node=% latex only
      \ifx\tikz@strokecolor@empty
        \xglobal\colorlet{draw color of \tikz@fig@name}{.}%
      \else
        \xglobal\colorlet{draw color of \tikz@fig@name}{\tikz@strokecolor}%
      \fi
    },
  save node fill color/.style={
    execute at begin node=% latex only
      \ifx\tikz@fillcolor@empty
        \xglobal\colorlet{fill color of \tikz@fig@name}{.}%
      \else
        \xglobal\colorlet{fill color of \tikz@fig@name}{\tikz@fillcolor}%
      \fi
    },
  save node concept color/.style={
    execute at begin node=% latex only
      \ifx\tikz@concept@color@empty
        \xglobal\colorlet{concept color of \tikz@fig@name}{.}%
      \else
        \xglobal\colorlet{concept color of \tikz@fig@name}{\tikz@concept@color}%
      \fi
    },
  save node colors/.style = {
    save node concept color,
    save node fill color,
    save node draw color,
    save node text color
  }
}
\makeatother
\DeclareDocumentCommand\info{m}{
    \node [
      annotation,
      right,
      draw = draw color of #1,
      text = text color of #1,
      fill = concept color of #1!10,
    ] 
    (#1-info) at (#1.east)
    {#1};
}
\begin{document}
  \begin{tikzpicture}[ 
    save node colors,
  ]
  %%% The Mindmap itsself
    \path[
      mindmap,
      concept color                 = root-color,
      every node/.style             = {
        concept,
      },
      root/.style                   = {
        text = root-textcolor,
      },
      level 1 concept/.append style = {
        sibling angle = 90,
      },
      level 2 concept/.append style = {
        sibling angle = 90,
      },
    ]
    node[root] (root) {Root}
    [clockwise from = 45]
    child[concept color = col1] {
      node (L1) {L1}
      child [concept color = violet] { node (L1-1) {L1-1} }
      child [concept color = orange] { node (L1-2) {L1-2} }
    }
    child[concept color = col2] {
      node (L2) {L2}
      child [concept color = purple] { node (L2-1) {L2-1} }
      child [concept color = teal] { node (L2-2) {L2-2} }
    }
  ;
%% Information nodes %%%%%%%%%%%%%%%%%%%%%%%%%%%%
  \info{root}
  \info{L1}
  \info{L1-1}
  \info{L1-2}
  \info{L2}
  \info{L2-1}
  \info{L2-2}
\end{tikzpicture}%
\end{document}