\documentclass{book}
\usepackage[scale=1,angle=0,opacity=1]{background}
\usetikzlibrary{calc}
\usepackage{ifthen}
\usepackage{lipsum}
\backgroundsetup{contents={}}
\pagestyle{plain}
% auxiliary counter
\newcounter{partshift}
\addtocounter{partshift}{-1}
\definecolor{mp}{RGB}{240,240,240}
\newcommand{\parttitle}{}
\makeatletter
\def\@part[#1]#2{%
\renewcommand\parttitle{#1}%
\ifnum \c@secnumdepth >-2\relax
\refstepcounter{part}%
\addcontentsline{toc}{part}{\thepart\hspace{1em}#1}%