Schraffur im Diagramm

\documentclass[a4paper]{scrartcl}
\usepackage{amssymb,amsmath}
\usepackage{graphicx} 
\usepackage{amsfonts}
\usepackage{verbatim}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}         % Umlaute wie ä,ö,ü, etc. können direkt eingegeben werden
\usepackage{ulem}
\usepackage{color}
\usepackage{geometry}
\usepackage{scrlayer-scrpage}
\usepackage{siunitx}
\usepackage{lastpage}
\usepackage{tikz}
\usetikzlibrary{arrows,intersections,patterns}
\begin{document}
\begin{tikzpicture}[
    thick,
    >=stealth',
    dot/.style = {
      draw,
      fill = white,
      circle,
      inner sep = 0pt,
      minimum size = 4pt
    }
  ]
  \coordinate (O) at (0,0);
  \draw[->,thick] (-0.3,0) -- (6,0) coordinate[label = {below:$t$}] (tmax);%x-Achse
  \draw[->,thick] (0,-0.3) -- (0,4.5) coordinate[label = {left:$v(t)$}] (vmax);%y-Achse
  \draw[pattern=north east lines, pattern color=red!20] (0,0)--(0,4)--(1,4)--(1,0) ;
  \draw[-,color=red] (0,4)--(1,4)--(1,0);
  \draw[pattern=north west lines, pattern color=blue!20] (0,0.75)--(5,0.75)--(5,0)--(0,0);
  \draw[-,color=blue] (0,0.75)--(5,0.75)--(5,0);
  \draw[-,thin] (1.5,0)--(1.5,0.75);
  \draw[-,thin] (4.5,0)--(4.5,0.75); 
  \path (1,0) node[dot, label = {below:$t_{L}$}]{};
  \path (1.5,0) node[dot, label = {below:$t_{1}$}]{};
  \path (5,0) node[dot, label = {below:$t_{S}$}]{};
  \path (5.5,0) node[dot, label = {below:$t_{2}$}]{};
  \path (0,4) node[dot, label = {left:$v_{L}$}]{};
  \path (0,0.75) node[dot, label = {left:$v_{S}$}]{};
 \end{tikzpicture}
\end{document}