\documentclass{article}

\usepackage{hhline}
\usepackage{color}
\usepackage{colortbl}

\definecolor{lightgray}{gray}{0.8}

\begin{document}
 \begin{tabular}{||l||r|r|r|r||}
   \doublerulesepcolor{white}
   \hhline{|t:=:t:====:t|}
   \rowcolor{lightgray} & \multicolumn{2}{c|}{\cellcolor{lightgray}\textbf{Experiment 050510-01}} & \multicolumn{2}{c||}{\cellcolor{lightgray}\textbf{Experiment 050616-01}}\\
   \hhline{||%
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   >{\doublerulesepcolor{lightgray}}%
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   \rowcolor{lightgray} & \textbf{\%Correct} & \textbf{Accuracy} & \textbf{\%Correct} & \textbf{Accuracy}\\
   \hhline{|:=::====:|}
   \textbf{Model M1} & 79 \% & 73 \% & 77 \% & 61 \%\\
   \hhline{||-||----||}
   \textbf{Model M3} & 88 \% & 37 \% & 82 \% & 60 \%\\
   \hhline{|b:=:b:====:b|}
 \end{tabular}
\end{document}
