\displaystyle{\partial_t \rho = - \nabla_{W_2} E(\rho) = \color{blue}{\nabla} \cdot \left(\rho \color{blue}{\nabla} \frac{\color{green}{\delta} E}{\color{green}{\delta} \rho}\right)}
\displaystyle{\partial_t \rho = - \nabla_{W_2} E(\rho) = \color{blue}{\nabla} \cdot \left(\rho \color{blue}{\nabla} \frac{\color{green}{\delta} E}{\color{green}{\delta} \rho}\right)}