\documentclass[11pt]{article}
\usepackage[svgnames]{xcolor}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage{amsfonts, amssymb, amsmath, amsthm,subeqnarray,dsfont}
\usepackage{multirow}
\usepackage{pgf,tikz,setspace}
\usepackage{setspace}
\usepackage[margin=2.5cm]{geometry}
\usepackage{natbib}
\usepackage{hhline}
\usepackage{url}
\usepackage{float,graphicx}
\usepackage[labelfont=bf]{caption}
\usepackage{subcaption}
\usepackage[pagebackref=true]{hyperref}
\usepackage{todonotes}
\usepackage{pgfplots}
\usepackage{comment}
\usepackage{pdflscape}
\usepackage{placeins}
\hypersetup{
    colorlinks=true,       % false: boxed links; true: colored links
    linkcolor=DarkBlue,          % color of internal links
    citecolor=DarkBlue,        % color of links to bibliography
    filecolor=DarkBlue,      % color of file links
    urlcolor=DarkBlue           % color of external links
}

\newcommand*{\blue}{\textcolor{blue}}
\newcommand*{\red}{\textcolor{red}}


\begin{document}

\spacing{1}

\vskip 15pt

\pgfmathdeclarefunction{gauss}{2}{%
  \pgfmathparse{1/(#2*sqrt(2*pi))*exp(-((x-#1)^2)/(2*#2^2))}%
}

\begin{tikzpicture}
\begin{axis}[
  no markers, domain=-4:10, samples=100,
  axis lines*=left, xlabel=$v^C$,
  every axis y label/.style={at=(current axis.above origin),anchor=south},
  every axis x label/.style={at=(current axis.right of origin),anchor=west},
  height=8cm, width=12cm,
  xtick={0,2,2.5,4}, ytick=\empty,
  enlargelimits=false, clip=false, axis on top,
  grid = major
  ]
  \addplot [fill=red!20, draw=none, domain=2.5:10] {gauss(4,2)} \closedcycle;
  \addplot [fill=cyan!20, draw=none, domain=2.5:10] {gauss(0,2)} \closedcycle;
  \addplot [very thick,cyan!50!black] {gauss(0,2)};
  \addplot [very thick,red!50!black] {gauss(4,2)};


\end{axis}
\end{tikzpicture}

\end{document} 