\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}

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.

\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>].