\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  G_{ur}(s) 
    = \frac{k_r}{1 + K G_{\hat x u}(s)}% \\
    = \frac{{\color{blue} k_r} (s^2 + l_1 s + l_2)}{s^2 + s(\gamma k_1 + k_2 + l_1) + k_1
      + l_2 + k_2 l_1 - \gamma k_2 l_2},
\end{equation*}
\end{document}