Wie kann ich die Fläche zwischen mehreren Pfaden mit Pfeilen kennzeichnen?

\documentclass[tikz, border=5pt]{standalone}   
\usepackage{tikz}
\usepackage{xparse}
\usetikzlibrary{backgrounds}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{
  arrows,
  decorations.pathreplacing,
  shapes.symbols,
  angles,
  quotes,
  calc,
  arrows.meta
}
\usepgfplotslibrary{fillbetween}

\NewDocumentCommand\DrawArrows{O{0.5}mmO{-latex}mm}{
\def\Step{#1}
\pgfmathsetmacro{\Second}{#5+\Step}
\foreach \Value [count=\xi] in {#5,\Second,...,#6}
  {
  \path[overlay,name path=line\xi] 
    (\Value,100) -- (\Value,-100);
  \path[name intersections={of=#2 and line\xi,by={1\xi}}];
  \path[name intersections={of=#3 and line\xi,by={2\xi}}];
  \ifdim#5pt<\Value pt\relax
    \ifdim\Value pt<#6pt\relax
    \draw[#4]
      (1\xi) -- (2\xi); 
  \fi\fi
  }
}

\begin{document}

    \begin{tikzpicture}
  \pgfdeclarelayer{pre main}
  \pgfsetlayers{pre main,main}
  % Koordinatensystem
  \coordinate (A) at (0, 0) {}; 
  \coordinate (B) at (10, 0) {}; 
  \coordinate (C) at (0, 9) {};
  \coordinate (D) at (4, 0) {};
  \coordinate (E) at (8, 0) {};
  \coordinate (I) at (0, 6) {};
  \coordinate (a) at (4, 6) {};
  \coordinate (b) at (8, 3) {};
  \coordinate (c) at (0, 2) {};
  \coordinate (d) at (9, 5) {};
  % Koordinatensystempfeile
  \draw[->,line width=0.4mm] (A) -- (B) node[below] {$v$};
  \draw[->,line width=0.4mm,name path=AtoC] (A) -- (C) node[left] {$F_\mathrm{T}$};
  % Koordinatenstriche
  \draw[-,line width=0.4mm] (D) -- (4, -0.1) node[below] {$v_\mathrm{ue1}$};
  \draw[-,line width=0.4mm] (E) -- (8, -0.1) node[below] {$v_\mathrm{max}$};
  \draw[-,line width=0.4mm] (I) -- (-0.1, 6) node[left] {$F_\mathrm{vue1}$};
  % Verbindungslinien
  \draw[dotted,name path=Dtoa] (D) -- (a);
  % Graphen
  \draw[name path=KurveI] (I) -- (a);
  \draw[name path=KurveII,bend left=20] (b) to (a);
  \draw[name path=KurveIII,dotted,bend left=20](d) to (c);

    \path [%draw,line width=3,blue,
    name path=IandIV,
    intersection segments={
        of=KurveI and AtoC,
        sequence={A1 -- B0[reverse]}
    }];

  \path [%draw,line width=3,blue,
    name path=IIIandII,
    intersection segments={
        of=KurveIII and KurveII,
        sequence={A1[reverse] -- B1}
    }];
   \path [%draw,line width=3,blue,
    name path=links,
    intersection segments={
        of=KurveIII and Dtoa,
        sequence={A1}
    }];

   \path [%draw,line width=3,blue,
    name path=rechts,
    intersection segments={
        of=KurveIII and Dtoa,
        sequence={A0}
    }];

  \pgfonlayer{pre main}
\DrawArrows[0.25]{KurveI}{links}[Stealth-Stealth,cyan]{0}{4.2} 
\DrawArrows[0.25]{KurveII}{rechts}[Stealth-Stealth,cyan]{4}{6.7} 
  \endpgfonlayer

\end{tikzpicture}

\end{document}