\midrule dashed and colored in booktabs -- two kinds of midrules in one booktab

You can use the tabu package instead:

\documentclass{beamer}          
\usepackage{tabu}

\begin{document}

\begin{frame}
\begin{table}
\tabulinesep =_4pt^4pt
\begin{tabu}to \textwidth{@{}cX[m]ccc@{}}
  \tabucline[1pt blue!40 off 0pt]{-}
  \multicolumn{2}{@{}l}{procesy} & Min & Max  &Dalkia\\
  \tabucline[0.7pt blue!40 off 0pt]{-}
  & Junior         & 1 700 & 2 800 & 3 200\\
  \tabucline[0.4pt blue!40 off 2pt]{-}
  & Senior         &  & ? &\\
  \tabucline[0.4pt blue!40 off 2pt]{-}
  & Specjalist     &  & ? &\\
  \tabucline[0.4pt blue!40 off 2pt]{-}
  & Team Leader    &  & ? &\\
  \tabucline[1pt blue!40 off 0pt]{-}
\end{tabu}
\caption{1. Wynagrodzenia: Procesy HR}
\label{tabela1}
\end{table}
\end{frame}

\end{document}

enter image description here


Here is an option that compares the tabu output of Gonzalo's answer with that of booktabs. It's workable in comparison with tabu, but it's not always pretty.

enter image description here

\documentclass{article}          
\usepackage{tabu}% http://ctan.org/pkg/tabu
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\usepackage{tabularx}% http://ctan.org/pkg/tabularx
\usepackage{booktabs}% http://ctan.org/pkg/booktabs
\makeatletter
\newcommand{\dashrule}[1][black]{%
  \color{#1}\rule[\dimexpr.5ex-.2pt]{4pt}{.4pt}\xleaders\hbox{\rule{4pt}{0pt}\rule[\dimexpr.5ex-.2pt]{4pt}{.4pt}}\hfill\kern0pt%
}
\newcommand{\rulecolor}[1]{%
  \def\CT@arc@{\color{#1}}%
}
\makeatother
\begin{document}

\begin{table}[t]
\tabulinesep =_4pt^4pt
\begin{tabu}to \textwidth{@{}cX[m]X[c]X[c]X[c]@{}}
  \tabucline[1pt blue!40 off 0pt]{-}
  \multicolumn{2}{@{}l}{procesy} & Min & Max  &Dalkia\\
  \tabucline[0.7pt blue!40 off 0pt]{-}
  & Junior         & 1 700 & 2 800 & 3 200\\
  \tabucline[0.4pt blue!40 off 2pt]{-}
  & Senior         &  & ? &\\
  \tabucline[0.4pt blue!40 off 2pt]{-}
  & Specjalist     &  & ? &\\
  \tabucline[0.4pt blue!40 off 2pt]{-}
  & Team Leader    &  & ? &\\
  \tabucline[1pt blue!40 off 0pt]{-}
\end{tabu}

\bigskip

\rulecolor{blue!40}
\begin{tabularx}{\linewidth}{X>{\centering}X>{\centering}X>{\centering\arraybackslash}X@{}}
  \toprule
  procesy & Min & Max & Delta \\
  \midrule
  Junior & 1\,700 & 2\,800 & 3\,200 \\[-\jot]
  \multicolumn{4}{@{}c@{}}{\makebox[\linewidth]{\dashrule[blue!40]}} \\[-\jot]
  Senior         &  & ? &\\
  \multicolumn{4}{@{}c@{}}{\makebox[\linewidth]{\dashrule[blue!40]}} \\[-\jot]
  Specjalist     &  & ? &\\
  \multicolumn{4}{@{}c@{}}{\makebox[\linewidth]{\dashrule[blue!40]}} \\[-\jot]
  Team Leader    &  & ? &\\
  \bottomrule
\end{tabularx}
\caption{1. Wynagrodzenia: Procesy HR}
\end{table}

\end{document}

The use of tabularx makes it convenient to specify the tabular width. Rule colour is specified using \rulecolor{<color>} and that of the dashed rule is done using \dashrule[<color>].