Intersection of double lines

Question

I'm trying unsuccessfully to fill the intersection of two double lines with an other colour. Here is minimal working example :

\documentclass{standalone}
\usepackage{tikz}


\begin{document}
    \begin{tikzpicture}

        \node (Emetteur) at (0,0) {};
        \node (Recepteur) at (2.5,0) {};
        \node (Recepteur2) at (-2.5,0) {};
        \node (Cible) at (1,3) {};

        \draw [black!15, double = black!15, double distance = 5] (1.25,0) ellipse (6cm and 3.025cm);
        \draw [black!15, double = black!15, double distance = 5] (-1.25,0) ellipse (6cm and 3.25cm);

        \draw (-4,0) -- (4,0);
        \draw (Emetteur) node {$\bullet$} node [below] {\'Emetteur};
        \draw (Recepteur) node {$\bullet$} node [below] {R\'ecepeur 1};
        \draw (Recepteur2) node {$\bullet$} node [below] {R\'ecepeur 2};
        \draw (Cible) node {$\bullet$} node [above=0.1cm, align = center] {Cible};

        \draw [blue] (Emetteur) -- (Cible) node [midway, sloped, above] {$d_1$};
        \draw [red] (Cible) -- (Recepteur) node [pos = 0.5, sloped, above] {$d_2$}; 
        \draw [green!50!black] (Cible) -- (Recepteur2) node [pos = 0.5, sloped, above] {$d_3$}; 


    \end{tikzpicture}
\end{document}

I get the following result :

I've found a way using the opacity option :

    \draw [black!15, double = black!50, double distance = 5, opacity = 0.2] (1.25,0) ellipse (6cm and 3.025cm);
    \draw [black!15, double = black!50, double distance = 5, opacity = 0.2] (-1.25,0) ellipse (6cm and 3.25cm);

Then I get :

That's just a trick since the superposition of two transparent shapes makes an other colour, but I prefer to avoid the opacity option since I get bad rendering when printing and I can't get an intersection of the colour I want.

Any clue ?

Answer 1

You can use blending

\begin{scope}[blend group=multiply]
        \draw [black!15, double = black!15, double distance = 5] (1.25,0) ellipse (6cm and 3.025cm);
        \draw [black!15, double = black!15, double distance = 5] (-1.25,0) ellipse (6cm and 3.25cm);
\end{scope}

Full code:

\documentclass{standalone}
\usepackage{tikz}


\begin{document}
    \begin{tikzpicture}

        \node (Emetteur) at (0,0) {};
        \node (Recepteur) at (2.5,0) {};
        \node (Recepteur2) at (-2.5,0) {};
        \node (Cible) at (1,3) {};
       \begin{scope}[blend group=multiply]
        \draw [black!15, double = black!15, double distance = 5] (1.25,0) ellipse (6cm and 3.025cm);
        \draw [black!15, double = black!15, double distance = 5] (-1.25,0) ellipse (6cm and 3.25cm);
    \end{scope}

        \draw (-4,0) -- (4,0);
        \draw (Emetteur) node {$\bullet$} node [below] {\'Emetteur};
        \draw (Recepteur) node {$\bullet$} node [below] {R\'ecepeur 1};
        \draw (Recepteur2) node {$\bullet$} node [below] {R\'ecepeur 2};
        \draw (Cible) node {$\bullet$} node [above=0.1cm, align = center] {Cible};

        \draw [blue] (Emetteur) -- (Cible) node [midway, sloped, above] {$d_1$};
        \draw [red] (Cible) -- (Recepteur) node [pos = 0.5, sloped, above] {$d_2$};
        \draw [green!50!black] (Cible) -- (Recepteur2) node [pos = 0.5, sloped, above] {$d_3$};


    \end{tikzpicture}
\end{document}