[Tex/LaTex] Set color of title-background

Question

I'm trying to give the title (and the title only (with some margin), not the entire page) in the first page of my presentation background color "greyone". This background-box should be page-wide while text is centered. I haven't been able to figure out how to..

I've defined a new beamer template in my preamble by

\documentclass['serif]{beamer}
\usecolortheme{eelke}
% INFORMATION
\title{Presentation Title}
\author{A. Uthor}
% FRONTPAGE
\defbeamertemplate*{title page}{eelke}[1]
{
\centering
\usebeamerfont{title}\inserttitle\par % this should have a background box in color grayone. Text should be white for readability.
\vskip20pt
\usebeamercolor[bg]{titlelike}
\setbeamerfont{author}{size=\fontsize{11}{15}}
\usebeamerfont{author}\insertauthor\par %
\vskip20pt
\setbeamerfont{date}{size=\fontsize{11}{15}}
\usebeamerfont{date}\insertdate\par} \begin{document}\begin{frame}\maketitle\end{frame}\end{document}

`

Further I have defined a new color in beamercolorthemeeelke.sty
file

\definecolor{greyone}{RGB}{77,77,77}
\setbeamercolor{palette quaternary}{fg=white,bg=greyone, wd=\paperwidth}
\setbeamercolor{titlelike}{parent=palette quaternary}

which is called for in the preamble: \usecolortheme{eelke}

Can anyone help me out?

Edit: MAW added

Answer 1

You can use a beamercolorbox but with beamerleftmargin and beamerrightmargin previously added to textwidth.

\documentclass['serif]{beamer}
%\usecolortheme{eelke}

\definecolor{greyone}{RGB}{77,77,77}
\setbeamercolor{palette quaternary}{fg=white,bg=greyone}
\setbeamercolor{titlelike}{parent=palette quaternary}

% INFORMATION
\title{Presentation Title}
\author{A. Uthor}
% FRONTPAGE
\makeatletter
\defbeamertemplate*{title page}{eelke}[1]
{
\@tempdima=\textwidth%
\advance\@tempdima by \beamer@leftmargin%
\advance\@tempdima by \beamer@rightmargin%
\begin{beamercolorbox}[sep=1em,wd=\the\@tempdima]{titlelike}
\centering
\usebeamerfont{title}\inserttitle\par % this should have a background box in color grayone. Text should be white for readability.
\end{beamercolorbox}
\vskip20pt
\usebeamercolor[bg]{titlelike}
\setbeamerfont{author}{size=\fontsize{11}{15}}
\usebeamerfont{author}\insertauthor\par %
\vskip20pt
\setbeamerfont{date}{size=\fontsize{11}{15}}
\usebeamerfont{date}\insertdate\par} 
\makeatother

\begin{document}
\begin{frame}
\maketitle
\end{frame}
\end{document}