To achieve the goal, you have to understand how the block colors are defined for the Boadilla theme.
Boadilla uses rose
as color theme in charge of customizing the blocks; it sets:
\setbeamercolor{block title}{use=structure,fg=structure.fg,bg=structure.fg!20!bg}
\setbeamercolor{block body}{parent=normal text,use=block title,bg=block title.bg!50!bg}
As you can see, the background color of the block body depends on the background color of the block title. So, basically, you want to reproduce in the block title the same color of the block body:
\setbeamercolor{block title}{fg=darkred,bg=structure.fg!20!bg!50!bg}
where: structure.fg!20!bg
is the original background block title color and !50!bg
is added to let him be exactly the color of the background block body. Now, the latter should be:
\setbeamercolor{block body}{use=block title,bg=block title.bg}
and that's it.
A complete example:
\documentclass[10pt,xcolor=dvipsnames,pdflatex]{beamer}
\usetheme{Boadilla}
\usecolortheme{beaver}
\definecolor{darkred}{rgb}{0.8,0,0}
\setbeamercolor{structure}{fg=darkred}
\setbeamercolor{block title}{fg=darkred,bg=structure.fg!20!bg!50!bg}
\setbeamercolor{block body}{use=block title,bg=block title.bg}
\begin{document}
\begin{frame}{My pink slide}
\begin{block}{Oh my god}\centering
this is so girlish.\\
Especially when\\
the block is\\
so big\\
that it\\
is close\\
to the\\
red/grey\\
frame title.
\end{block}
\vfill
\begin{block}{}
Nice, bright block!\\
I like this and would not change its bg color.
\end{block}
\end{frame}
\end{document}
The result:
So this may not be what you need since I don't know where you are starting:
\documentclass{beamer}
\title{Title}
\author{Me}
\begin{document}
\setbeamertemplate{navigation symbols}{}
\setbeamertemplate{background}{\includegraphics[width=\paperwidth,height=\paperheight]{teitl}}
\frame[label=title]{\titlepage}
\setbeamertemplate{background}{\includegraphics[width=\paperwidth,height=\paperheight]{tudalen}}
\begin{frame}{Frame Title}
This is a regular page.
\end{frame}
\end{document}
Update
The only way I can currently figure to do this is as follows:
\documentclass{beamer}
\usetheme{Atlanta}
\makeatletter
\defbeamertemplate*{frametitle}{mytitle}[1][left]
{
\ifbeamercolorempty[bg]{frametitle}{}{\nointerlineskip}%
\@tempdima=\textwidth%
\advance\@tempdima by\beamer@leftmargin%
\advance\@tempdima by\beamer@rightmargin%
\begin{beamercolorbox}[sep=0.3cm,#1,wd=\the\@tempdima]{}
\usebeamerfont{frametitle}%
\vbox{}\vskip-1ex%
\if@tempswa\else\csname beamer@fte#1\endcsname\fi%
\strut\insertframetitle\strut\par%
{%
\ifx\insertframesubtitle\@empty%
\else%
{\usebeamerfont{framesubtitle}\usebeamercolor[fg]{framesubtitle}\insertframesubtitle\strut\par}%
\fi
}%
\vskip-1ex%
\if@tempswa\else\vskip-.3cm\fi% set inside beamercolorbox... evil here...
\end{beamercolorbox}%
}
\makeatother
\setbeamertemplate{footline}{}
\setbeamertemplate{frametitle}[mytitle]
\title{Title}
\author{Me}
\begin{document}
\setbeamertemplate{navigation symbols}{}
\setbeamertemplate{background}{\includegraphics[width=\paperwidth,height=\paperheight]{teitl}}
% plain removes the navigation bar etc.
\frame[plain]{\titlepage}
\setbeamertemplate{background}{\includegraphics[width=\paperwidth,height=\paperheight]{tudalen}}
\begin{frame}{Frame Title}
This is a regular page.
\end{frame}
\end{document}
Update to Update
\documentclass[font=9pt]{beamer}
\usetheme{Atlanta}
\makeatletter
\defbeamertemplate*{frametitle}{mytitle}[1][left]
{
\ifbeamercolorempty[bg]{frametitle}{}{\nointerlineskip}%
\@tempdima=\textwidth%
\advance\@tempdima by\beamer@leftmargin%
\advance\@tempdima by\beamer@rightmargin%
\begin{beamercolorbox}[sep=0.3cm,#1,wd=\the\@tempdima]{}
\usebeamerfont{frametitle}%
\vbox{}\vskip-1ex%
\if@tempswa\else\csname beamer@fte#1\endcsname\fi%
\strut\insertframetitle\strut\par%
{%
\ifx\insertframesubtitle\@empty%
\else%
{\usebeamerfont{framesubtitle}\usebeamercolor[fg]{framesubtitle}\insertframesubtitle\strut\par}%
\fi
}%
\vskip-1ex%
\if@tempswa\else\vskip-.3cm\fi% set inside beamercolorbox... evil here...
\end{beamercolorbox}%
}
\makeatother
\setbeamertemplate{footline}{}
\setbeamertemplate{frametitle}[mytitle]
\setbeamertemplate{headline}{}% eliminate headline so background is revealed
\definecolor{myblue}{rgb}{0.4, 0.6, 0.8}% adjust as desired
\setbeamercolor{structure}{fg=myblue}
\defbeamertemplate*{title page}{customized}[1][]
{
\usebeamerfont{title}\inserttitle\par
\usebeamerfont{subtitle}\usebeamercolor[fg]{subtitle}\insertsubtitle\par
\bigskip
\usebeamerfont{author}\insertauthor\par
\usebeamerfont{institute}\insertinstitute\par
\usebeamerfont{date}\insertdate\par
\usebeamercolor[fg]{titlegraphic}\inserttitlegraphic
}
%\usepackage{Warsaw}
%\usepackage{beamercolorthemeyellowjacket}
\usefonttheme{serif}
\usepackage{amsmath,amssymb,amsthm,amsfonts}
\usepackage{algorithmic,algorithm}
\usepackage{graphicx,ifpdf}
\usepackage{mathrsfs}
\usepackage{natbib}
\usepackage{dsfont}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage{times}
\usepackage{verbatim}
\usepackage{multirow}
\usepackage{multicol}
\usepackage{algorithm}
\usepackage{algorithmic}
\usepackage{booktabs}
\usepackage{caption}
\usepackage{subcaption}
\usepackage{wasysym}
\usepackage{tabularx}
\usepackage{tabulary}
\def\Ze{\mathbb{Z}}
\def\Qe{\mathbb{Q}}
\def\Re{\mathbb{R}}
\def\Ne{\mathbb{N}}
\def\E{\mathbb{E}}
%\def\Pr{{\rm Pr}}
\def\newblock{}
\DeclareMathOperator*{\wg}{\wedge}
\newcommand{\set}[1]{\left\{ #1 \right\}}
\newtheorem{thm}{Theorem}
\newtheorem{lem}{Lemma}
\newtheorem{obs}{Observation}
\newtheorem{prop}{Proposition}
\newtheorem{cor}{Corollary}
\newtheorem{dfn}{Definition}
\newtheorem{asp}[theorem]{Assumption}
\newcommand{\rv}{\mathcal{T}}
\newcommand{\rr}{\mathbb{R}}
\newcommand{\zz}{\mathbb{Z}}
\newcommand{\nn}{\mathbb{N}}
\newcommand{\rw}{W}
\newcommand{\rc}[1]{\textcolor{Black}{#1}}
\newcommand{\bc}[1]{\textcolor{Black}{#1}}
\title[Presentation ] % (optional, use only with long paper titles)
{Presentation Title}
\institute[my institute]{
}
\author[my name ] % (optional, use only with lots of authors)
{my name}
\date[]
\begin{document}
\setbeamertemplate{navigation symbols}{}
\setbeamertemplate{background}{\includegraphics[width=\paperwidth,height=\paperheight]{blue}}
\frame[plain]{\titlepage}
\setbeamertemplate{background}{\includegraphics[width=\paperwidth,height=\paperheight]{background}}
\begin{frame}\frametitle{Outline}
\begin{enumerate}
\item Introduction
\item A two-stage chance-constrained model
\item Case study
\item Solution approaches
\item Conclusions
\end{enumerate}
\end{frame}
\section{Introduction}
\begin{frame}\frametitle{}
\begin{center}
\bfseries{Thank you!}\\
\vspace{2cm}
\bfseries{Comments?}\\
\end{center}
\end{frame}
\section{A two-stage chance-constrained model}
\begin{frame}\frametitle{}
\begin{center}
\bfseries{Thank you!}\\
\vspace{2cm}
\bfseries{Comments?}\\
\end{center}
\end{frame}
\section{Case study}
\begin{frame}\frametitle{}
\begin{center}
\bfseries{Thank you!}\\
\vspace{2cm}
\bfseries{Comments?}\\
\end{center}
\end{frame}
\section{Solution approaches }
\begin{frame}\frametitle{A Frame Title}
\begin{center}
\bfseries{Thank you!}\\
\vspace{2cm}
\bfseries{Comments?}\\
\end{center}
\end{frame}
\end{document}
Best Answer
With this: (taken from here Changing default width of blocks in beamer)
Result: