\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  \aligned 
    \frac{dz}{dt} &= y - v_r, \qquad
    {\color{blue} w} &= -k_p x - k_i z + k_r v_r,
  \endaligned
\end{equation*}
\end{document}