\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  G_{y r} = \frac{P(s) {\color{blue} G_{ur}(s)}}{1 {\color{blue} -} P(s) G_{uy}(s)} 
    = \frac{{\color{blue} k_r} (\gamma s + 1)}{s^2 + (k_1 \gamma + k_2) s + k_1}.
\end{equation*}
\end{document}