[Tex/LaTex] How to change color of the title and add a line on the title-page in beamer

Question

I would like to change the the blue box behind the title on title page to be white and the color the title to be black.

Furthermore, I would like to add a straight orange horizontal line in between the title and the author. The ideal end result looks like this:

The original codes are below:

\documentclass{beamer}

\mode<presentation> {
\usetheme{Madrid}
\setbeamertemplate{footline}[page number]
\setbeamertemplate{navigation symbols}{}
}

\usepackage{graphicx}
\usepackage{booktabs}


\title[Short title]{Main Topic }
\author{John Smith}
\institute[UCLA]
{
University of California \\
\medskip
\textit{john@smith.com}
}
\date{\today}


\begin{document}

\begin{frame}
\titlepage
\end{frame}


\section{First Section}
\begin{frame}
\frametitle{Paragraphs of Text}
Sed 
\end{frame}

\end{document}

Thank you very much!

Answer 1

You can redefine the title page as follows:

\documentclass{beamer}

\mode<presentation> {
    \usetheme{Madrid}
    \setbeamertemplate{footline}[page number]
    \setbeamertemplate{navigation symbols}{}
}

\usepackage{graphicx}
\usepackage{booktabs}
\usepackage{datetime}

\makeatletter
\setbeamertemplate{title page}
{
    \vbox{}
    \vfill
    \begingroup
    \centering
    \begin{minipage}{.9\linewidth}
    \usebeamerfont{title}\textsc{\inserttitle}\par
    \ifx\insertsubtitle\@empty%
    \else%
    \vskip0.25em%
    {\usebeamerfont{subtitle}\insertsubtitle\par}%
    \fi%
    \vspace{1.7em}
    {\color{orange}\hrule}\vspace{1.7em}
    \usebeamerfont{author}\insertauthor\par\vspace{.7em}
    \usebeamerfont{date}\insertdate\par
    \end{minipage}\par
    \endgroup
    \vfill
    \thispagestyle{empty}
}
\makeatother


\title[Short title]{Main Topic}
\author{John Smith}
\institute[UCLA]
{
    University of California \\
    \medskip
    \textit{john@smith.com}
}
\date{\shortmonthname\space\the\year}


\begin{document}

\begin{frame}
    \titlepage
\end{frame}


\section{First Section}
\begin{frame}
\frametitle{Paragraphs of Text}
Sed 
\end{frame}

\end{document}

Of course, you could change the font for the author and date to serifs, if desired:

\setbeamerfont{author}{family=\rmfamily}
\setbeamerfont{date}{family=\rmfamily}