Tricolored Rectangle Using Tikz

Question

I am trying to create a tricolored rectangle in which I can specify the point where the color changes (i.e. not necessarily equally spaced like the French flag). I have included a MWE below that colors the rectangle uniformly and an image of the desired result.

\documentclass[tikz,margin=2mm]{standalone}
\begin{document}
\begin{tikzpicture}
\node [rectangle, minimum width=2cm, fill=blue] (A) {}
\end{tikzpicture}
\end{document}

Answer 1

It's not very difficult to make a \pic which draws the rectangle and its three parts. This way you can put nodes in it at your desired positions.

For example, the code:

\documentclass[border=2mm,tikz]{standalone}

\tikzset
{% USAGE:
 % #1 = rectangle width
 % #2 = rectangle height
 % #3 = relative position of the first  division (0-1), between left   and middle rectangles
 % #4 = relative position of the second division (0-1), between middle and right  rectangles
 % #5 = left   part color
 % #6 = middle part color
 % #7 = right  part color
  pics/tricolor/.style n args={7}{%
    code={%
      \path[fill=#5] (0,0)     rectangle (#1*#3,#2);
      \path[fill=#6] (#1*#3,0) rectangle (#1*#4,#2);
      \path[fill=#7] (#1*#4,0) rectangle (#1,#2);
      \draw (0,0) rectangle (#1,#2);
      \draw (#1*#3,0) --+ (0,#2);
      \draw (#1*#4,0) --+ (0,#2);
      \coordinate (-left)   at (0.5*#1*#3       ,0.5*#2);
      \coordinate (-middle) at ({0.5*#1*(#3+#4)},0.5*#2);
      \coordinate (-right)  at ({0.5*#1*(#4+1)} ,0.5*#2);
    }}
}

\begin{document}
\begin{tikzpicture}
\pic (A) {tricolor={6}{1}{0.15}{0.6}{green!70!black}{red}{yellow}};
\node at (A-left)   {left};
\node at (A-middle) {middle};
\node at (A-right)  {right};

\pic (B) at (0.5,-4) {tricolor={5}{3}{0.33}{0.67}{blue!80}{white}{red}};
\node at (B-left)   {Vive};
\node at (B-middle) {la};
\node at (B-right)  {France};
\end{tikzpicture}
\end{document}

Will produce:

Edit: Introducing rounded corners, as requested. I draw first the left and right rectangles bigger and with rounded corners (as an option passed to the \pic) and then the center rectangle over them and without rounded corners.

Note that if the radii of the corners is bigger than the width of the center rectangle it will not look good.

\documentclass[border=2mm,tikz]{standalone}

\tikzset
{% USAGE:
 % #1 = rectangle width
 % #2 = rectangle height
 % #3 = relative position of the first  division (0-1), between left   and middle rectangles
 % #4 = relative position of the second division (0-1), between middle and right  rectangles
 % #5 = left   part color
 % #6 = middle part color
 % #7 = right  part color
  pics/tricolor/.style n args={7}{%
    code={%
      \path[fill=#5]                   (0,0)     rectangle (#1*#4,#2);
      \path[fill=#7]                   (#1*#3,0) rectangle (#1,#2);
      \path[fill=#6,rounded corners=0] (#1*#3,0) rectangle (#1*#4,#2); % this rectangle without rounded corners
      \draw (0,0) rectangle (#1,#2);
      \draw (#1*#3,0) --+ (0,#2);
      \draw (#1*#4,0) --+ (0,#2);
      \coordinate (-left)   at (0.5*#1*#3       ,0.5*#2);
      \coordinate (-middle) at ({0.5*#1*(#3+#4)},0.5*#2);
      \coordinate (-right)  at ({0.5*#1*(#4+1)} ,0.5*#2);
    }}
}

\begin{document}
\begin{tikzpicture}
\pic[rounded corners=0.5cm] (B) at (0.5,-4) {tricolor={5}{3}{0.33}{0.67}{blue!80}{white}{red}};
\node at (B-left)   {Vive};
\node at (B-middle) {la};
\node at (B-right)  {France};
\end{tikzpicture}
\end{document}

Answer 2

You can use a matrix with equal height nodes

\documentclass[border=2mm, tikz]{standalone}
\usetikzlibrary{matrix}

\begin{document}
\begin{tikzpicture}
\matrix (A) [matrix of nodes, inner sep=0pt, draw, nodes={anchor=center, inner sep=0.3333em, minimum height=1cm}, row sep=-\pgflinewidth]
{|[fill=red!30]|This is\strut & |[fill=green!30]| a tricolor\strut & |[fill=blue!30]| node (or matrix)\\};
\end{tikzpicture}
\end{document}

Answer 3

This is a rework of my previous answer in https://tex.stackexchange.com/a/566081/38080... with a rectangle is easier. Just use the calc intermediate coordinates (remember: ($(A)!x!(B)$) is a point on the line from (A) to (B), where x is the relative position: x=0 is the same as (A), x=0.5 is midway etc...)

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,calc,backgrounds}
\begin{document}
\begin{tikzpicture}[
    ]
    % draw the node with no background
    \node[draw] (R) {divided by 20\%, 30\%, 50\%};
    % and after that...
    \begin{scope}[on background layer]
        \fill [green!20] (R.south west) rectangle ($(R.north west)!.2!(R.north east)$);
        \fill [orange!20] ($(R.south west)!.2!(R.south east)$) rectangle ($(R.north west)!.5!(R.north east)$);
        \fill [purple!20] ($(R.south west)!.5!(R.south east)$) rectangle (R.north east);
    \end{scope}
\end{tikzpicture}
\end{document}

You can easily wrap this in a macro if you like.