Cfrgtkky

In an answer to a previous question (Drawing curves with LaTeX), this curve was drawn

documentclass[tikz,border=3.14mm]{standalone}

usetikzlibrary{decorations.markings}

begin{document}

begin{tikzpicture}[set mark/.style args={#1 at #2}{postaction={decorate,

decoration={markings,mark=at position #2 with #1}}}]

 begin{scope}[xshift=10cm]

   draw[set mark={{node at (0,0.3) {1};}} at 0,set mark={coordinate (1);} at 0.25,

  set mark={{node at (0,0.3) {2};}} at 0.5,set mark={coordinate (2);} at 0.75] plot[smooth cycle,tension=1.1] coordinates {(60:1) (-70:1) (-120:1) (110:1)};

  draw (1) to[out=30,in=150] node[midway,below right] {3} (2);

 end{scope}

end{tikzpicture}

end{document}

Is it possible to rewrite the code above in order to put colors in the regions of the space divided by the curve?

Here is a solution based on fillbetween. In this case you could also work with clip, but in general this won't work.

documentclass[tikz,border=3.14mm]{standalone}

usetikzlibrary{decorations.markings,backgrounds}

usepackage{pgfplots}

pgfplotsset{compat=1.16}

usepgfplotslibrary{fillbetween}

begin{document}

begin{tikzpicture}[set mark/.style args={#1 at #2}{postaction={decorate,

decoration={markings,mark=at position #2 with #1}}}]

 begin{scope}[local bounding box=graph]

   draw[set mark={{node at (0,0.3) {1};}} at 0,set mark={coordinate (1);} at 0.25,

  set mark={{node at (0,0.3) {2};}} at 0.5,set mark={coordinate (2);} at 0.75,

  name path global=contour]

   plot[smooth cycle,tension=1.1] coordinates {(60:1) (-70:1) (-120:1) (110:1)};

  draw[name path global=divide] (1) to[out=30,in=150] node[midway,below right] {3} (2);

 end{scope}

 begin{scope}[on background layer]

  fill[blue,intersection segments={of=contour and divide,

 sequence={L*}}];

  fill[red,intersection segments={of=contour and divide,

 sequence={R2--L2[reverse]}}];

 end{scope}

end{tikzpicture}

end{document}

And as for your comment here, this is a way to attach arrows to the divide line.

documentclass[tikz,border=3.14mm]{standalone}

usetikzlibrary{decorations.markings,backgrounds}

usepackage{pgfplots}

pgfplotsset{compat=1.16}

usepgfplotslibrary{fillbetween}

begin{document}

begin{tikzpicture}[set mark/.style args={#1 at #2}{postaction={decorate,

decoration={markings,mark=at position #2 with #1}}},

attach arrow/.style={set mark={{draw[-latex] (0,0.3) -- (0,0);}} at #1}]

 begin{scope}[local bounding box=graph]

   draw[set mark={{node at (0,0.3) {1};}} at 0,set mark={coordinate (1);} at 0.25,

  set mark={{node at (0,0.3) {2};}} at 0.5,set mark={coordinate (2);} at 0.75,

  name path global=contour]

   plot[smooth cycle,tension=1.1] coordinates {(60:1) (-70:1) (-120:1) (110:1)};

  draw[name path global=divide,attach arrow/.list={0.1,0.2,...,0.9}] (1) to[out=30,in=150] node[midway,below right] {3} (2);

 end{scope}

 begin{scope}[on background layer]

  fill[blue,intersection segments={of=contour and divide,

 sequence={L*}}];

  fill[red,intersection segments={of=contour and divide,

 sequence={R2--L2[reverse]}}];

 end{scope}

end{tikzpicture}

end{document}

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