\documentclass[tikz,border=12pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
   %\usepgfplotslibrary{external}
%\tikzexternalize
\begin{document}
\def\firstcircle{(0.75,0) circle (2.5cm)}
  \def\secondcircle{(0.5,0) circle (2.5cm)}
  \def\thirdcircle{(0.25,0) circle (2.5cm)}
  \def\fourthcircle{(0,0) circle (2.5cm)}
%\tikzsetnextfilename{4way_venn}
    \begin{tikzpicture}
\begin{scope}[ fill opacity=0.5]
        \fill[gray] \firstcircle;
        \fill[gray] \secondcircle;
        \fill[gray] \thirdcircle;
    \fill[opacity=1,white] \fourthcircle;\end{scope}
%    \begin{scope}
%      \clip \firstcircle;
%      \clip \secondcircle;
%      \clip \thirdcircle;
%\fill[cyan]\fourthcircle;
%    \end{scope}
      \draw \firstcircle {};
      \draw \secondcircle {};
      \draw \thirdcircle {};
      \draw \fourthcircle node [text=black, text width=2cm, align=center]{Aircrafts};

    \end{tikzpicture}
\end{document}