Graphics, Figures & Tables ⇒ remove space between merged rows

[amshahraki]

I am trying to change the color of rows in a longtable latex. The problem is that, I have merged some rows but when I change the background color of cells there is a space between merged rows which is white. You can see it in screenshot.
Here is the code of my header

\begin{scriptsize}

\setlength\tabcolsep{5pt}



\begin{longtable}{|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|}




\caption{Clustering Techniques}
\label{clusteringtechs}

\hline
\multirow{2}{*}{\#} &
\multirow{2}{*}{\begin{tabular}[c]{@{}l@{}}Clustering\\ Technique\end{tabular}} & \multirow{2}{*}{Year} & \rotatebox{90}{\multirow{2}{*}{\begin{tabular}[c]{@{}l@{}}Support\\Heterogeneity\end{tabular}}} & 
\multicolumn{2}{c|}{\begin{tabular}[c]{@{}c@{}}Role\\ of\\ CH\end{tabular}}&\rotatebox{90}{\centering \multirow{2}{*}{Routing}} &
\rotatebox{90}{\multirow{2}{*}{\begin{tabular}[c]{@{}l@{}}support\\Mobility\end{tabular}}} & \multicolumn{17}{c|}{Objectives} \\ \cline{5-6} \cline{9-25} 
 &  &  &  & \rotatebox{90}{Relay} & \rotatebox{90}{Fusion} &  &  & E & L & R & D & J & T & Y & P & C & O & F & B & A & M & S & U & H \\ \hline
 \endhead
 \toprule