\documentclass{article}
\usepackage{graphicx}
\usepackage{color}
\begin{document}
\thispagestyle{empty}
\fboxrule=0.0mm
%\fboxsep=1mm
\colorbox[gray]{1.0}{\parbox[c][5mm][c]{35mm}{
$$
	\mbox{DIC} = 2 \overline{D(\phi)} - D(\overline{\phi})
$$
}}
\end{document}